Trying to work out what this might be a symptom of. I find that whilst cycling, my right foot is constantly seeking to push forward in the shoe, and I kind of scrunch my toes (big toe esp) like I’m clawing at the bottom front of the shoe. I’ve had this in various brands/shoes so not sure it’s a ‘wrong size shoe’ problem, though I guess it could be. Any thoughts on what this might relate to and how to alleviate?
When your toes are trying to grip something inside the shoe it is usually a case of a poor fit. Not necessarily a size issue although it might be - most common would be too large or wide. A custom footbed and the right size shoe will work wonders. Your foot should be able to naturally flatten out when weight bearing and not be seeking stabilization. I bring this up as a downhill skier who has obsessed over the right ski boots as much as I obsess over my bike fit. The difference is huge when you get it right in both sports.
You must be riding with a pronounced toedown.
Suggest using lower stack pedals and shoes, moving your cleats back and lowering your seat a bunch.
I definitely have a pronounced toedown when pedalling. However I’ve dropped my saddle significantly over the past 12 months and though I’m sure it’s helped, I believe that’s just my style. My cleats are pretty much jammed all the way back already too. Perhaps I’ll play around with both again to see if I can come up with anything that improves things. Else, maybe it is a (shoe) fit issue, and my right foot has some discrepancy vs. left.
I ride toe down as well and I’m always trying to drive my big toe threw the bottom of the shoe… Starts really huting after a while. Doesn’t matter how much I lower my seat still toe down.
I mentioned this very thing to my fit guy, when I bought my bike last spring. It’s been a PITA my whole cycling career, going back to the 80’s. He put a metitarsal spreading insole under my toes, and I’ll be darned, they feel great, and this has been the most comfortable summer of cycling I’ve, had in many years.
IMO the cleats should be placed far forward to eliminate this. Not far back.
Correct cleat positioning is key to have an efficient pedal stroke.
I’m sure some bike fitters will suggest to get an appropriate fit.
Louis 
You must be riding with a pronounced toedown.
Suggest using lower stack pedals and shoes, moving your cleats back and lowering your seat a bunch.
Toe down isn’t always a sign of a saddle being too high. Start with a rider in a traditional road fit with feet parallel to the ground at full extension. Move the rider to a steeper position. This is a bit like rotating the rider around the bottom bracket. The saddle has to be raised just a bit to keep the knee at the same angle when the leg is extended. Since the saddle is now closer to the pedal (from front to rear), with no other changes, the rider’s toes are now likely to point down. I can only see two things to change that; move the cleats rearward or the rider now has to bend her or his ankle more acutely.
But, I could have missed something… Wouldn’t be the first time… Today…
You must be riding with a pronounced toedown.
Suggest using lower stack pedals and shoes, moving your cleats back and lowering your seat a bunch.
Toe down isn’t always a sign of a saddle being too high. Start with a rider in a traditional road fit with feet parallel to the ground at full extension. Move the rider to a steeper position. This is a bit like rotating the rider around the bottom bracket. The saddle has to be raised just a bit to keep the knee at the same angle when the leg is extended. Since the saddle is now closer to the pedal (from front to rear), with no other changes, the rider’s toes are now likely to point down. I can only see two things to change that; move the cleats rearward or the rider now has to bend her or his ankle more acutely.
But, I could have missed something… Wouldn’t be the first time… Today…
Far forward cleats tend to make the foot lock up into a stable whole to support itself while being highly leveraged from the front.
If cleats are moved back and the foot does become flatter, there will be quite a large change in seat height needed and the seat height itself may just be causing him to reach with he foot in the first place.
Cheap thick shoes tend to do the same.
Another avenue to explore is to get a shoe with more lengthwise curve to it from the cleat to toe so that it supports the front of the foot from moving forwards under load.