As I found when I started my journey without laces, skating backwards was a totally different kettle of fish than skating forward. Sure, I could glide backwards, do crossovers and turns and stops without any issues but as soon as I really drove hard onto the inside edge to generate power, my foot (due to my pronation) would collapse on me. This was still going on a long time after I had pretty much mastered my forward skating without laces. Even today I still get caught out occasionally, on my last skate 2 weeks ago I was at a stick and puck doing 1 on 1 D work against some ex pros, every now and then when I drove hard off the inside edge it would partially collapse on me. Backward skating power moves are the ones that expose any weakness in your foot mechanics the most. As you can skate without laces / untied I'd suggest that, once rinks are open again, go for a skate this way. If you find your foot collapsing on you doing whatever move it is that causes the pain then this is a good guide as to where you need to do extra work to correct it.