Hi,
The problem is likely to be that you are sliding forward in the boot, causing impact of the toes into the toe box of the boot. The boots may have a crowded toe box or be badly designed with a internal seam.
A number of possible solutions.
1. Make sure your toe nails are clipped - long nails increase the problem.
2. Check the inside of the toe box for excessive seams - run your finger inside the boots.
3. Check your socks for excessive seams or to stop the sock sliding into the toe box if bulky or too loose.
4. Most likely remedy - tighten the lacing across your instep to ensure that your heel is held firmly into the heel counter of the boot to stop your feet sliding forward in the boot when you stop or change direction.
Hope this helps.
MrPhysio+