Either you are in a deficit or you are not. Plateaus for 6 weeks are rough...but something isn't adding up and it isn't magic, or a refeed, or that you aren't "cheating correctly". Ethiopians don't get cheat meals and they still get ripped to the bone. The laws of thermodynamics are probably more proven than the laws of gravity so I doubt you have found a way to get around it. The endocrine system (hormones) are a slave to these laws just like everything else, they CANNOT overcome them.
First off - are you natural? Because, 215 @ 5'10'' and 24% bodyfat naturally is pretty well trained TBH. Maybe a lot of us don't think so, but according to BMI the MOST anyone 5'11'' should weigh to be healthy is 175-180#. If you've achieved this at 10% bodyfat, you'd have a pretty impressive physique with 162 pounds of lean mass. This may not seem impressive given the world we live in today, but being above "normal weight" BMI range and being lean is not something you see very often in a natural. It's pretty rare and would require a lot (years) of hard work and effort. Not questioning that you aren't above average, you may be - just a reality check there for you to look at yourself and where you are in the journey and see if this describes you. Calipers are often wrong, and lean mass will have a large impact on your metabolism.
Now, ignoring all of that - BMR calculators show someone 215 @ 5'11'' will burn between 2,000 - 2,200 calories/day depending on their age.
You walk, assuming 3.5 miles an hour which is pretty brisk, on an incline for 45 minutes 3X/week. This should be 2.25 miles roughly each time, 6.75 miles per week @ lets say 110 calories/mile = 742.5 calories. Minus about 340 calories that you would have burned doing nothing for the same amount of time as it is already accounted for in your BMR = 403 calories/week burned.
You do 3 HIIT sessions per week, assuming 20 minutes, and let's assume you average 13 calories/minute (pretty darn intense) = 260 calories X 3 = 780 calories. Minus 92 calories already accounted for in the BMR = 688.
You do 5 weight training sessions per week, which I will assume last 45 minutes and burn about 350 calories each = 1,750 calories. Minus 344 calories already accounted for in your BMR = 1,406 calories/week.
This yields 2,497 calories burned through exercise per week.
Plus your BMR of 2,200 x 7 = 15,400 calories/week
Total = 17,897 calories/week to maintain your weight.
Let's call it 20,000 calories/week to account for other unaccounted for activities (about 350 calories a day extra) (2,857 calories/day).
You're eating 2,170 calories/day.
This is a deficit of 687 calories/day X 7 = 4,810 calories/week (divided by 3,500 calories/pound bodyfat) = 1.37 pounds of bodyfat loss per week.
Here is the thing though - how are you factoring in the cheats? Because it's REAL easy to have a cheat with 2,000 calories in it and suddenly you're down to 0.8 pounds of fat loss per week instead of 1.37.
Next, how are you weighing yourself? How often? Everyone says to just weigh yourself once per week, and I am the crazy psycho that says to weigh yourself AT LEAST 1X per day. Best bet, wake up every morning, take a leak, take off your clothes, step on the scale. You may just be weighing yourself at different times and not realizing you are losing weight. You could drink a quart of water during a workout and gain 2 pounds right there. If you're losing less than 2 pounds a week of fat...water could easily wipe it out if you don't know you're at a peak or a trough.
Next, plateaus are not always plateaus. More than 3 weeks, IMO, means that something is wrong and not being accounted for - but it is typical to be doing everything right and you don't see much (or even may think you're gaining) for a week or even 2, and then suddenly you lose a bunch of water retention and you're 5 pounds lighter. 6 weeks is a bit long though.
Also, it sounds like you're afraid to cut calories. You are relying on exercise to create a deficit, which I am a firm believer, is a big mistake. We always over estimate how many calories we burn during exercise and how much impact it has. Exercise has one purpose during a cut - maintain muscle mass. It is so hard to burn calories through exercise that it really should be kept to a minimal. You are not going crazy, I've seen worse. But it's worth looking at.
And you said something interesting - you started gaining muscle at the beginning of the cut. To me this implies a few things. The first is, that you may not be accustomed to weight training. Gaining muscle in a caloric surplus is tough. Gaining it in a deficit is pretty unusual if you are natural and accustomed to training. If it is new to your body, the novelty gains may come even in a deficit but that's usually the only scenario this happens.
Alongside this point, if you are not trained and you are natural and you're 5'11'' and 215 - I highly doubt you're 24% bodyfat. You likely carry less muscle than you expect and thus have a lower metabolism than you realize.
The other thing it makes me wonder - maybe you are trained and you STILL saw gains at the beginning of the diet. This, to me, implies that you were not in a very big deficit (if at all) and your metabolism is slower than you think, simply because most people will see their biggest drops in strength at the beginning of a diet, say the first 2 weeks, as glycogen stores deplete a little and your body swaps energy production around. Sure you lost 10 pounds...but a lot of that could just have been water weight or even food weight if you weren't dieting.
If this were me, I would drop some of the exercise - say weights 4 times per week, 2 HIIT sessions, and whatever you think on casual walks. Maybe even drop the incline on the walks. Make them easy and low intensity. Then I would drop maybe 200 calories a day from the diet side and see where that leaves you in a week or two.
For the most part I think you are doing A LOT of things right - and it seems like you've stuck to it for 6 weeks and you're getting the basics down (track, weigh, measure). You're also putting in a lot of work.
Maybe you're closer than you think to seeing results, and the strength drop is just because you're hitting more of a deficit the last couple weeks. Maybe the first 3 weeks you weren't as methodical and things weren't as tight and with a couple weeks of practice and getting better at sticking to the diet you've finally approached where your deficit is and now you're seeing the strength drop.
Calipers are good - another simple thing to do is to measure your stomach with a tape measure regularly. This can be very very telling. Sometimes calipers can't tell the difference yet, the scale doesn't move, but your gut get smaller.
My numbers are estimates above, they could be wrong, hopefully it lays out a thought process and you can plug in new numbers and play around. Not sure any of this is THE answer, but hopefully it gets some ideas out there and helps. I bet, with all that you're doing right, you are not too far off.