If it is the pulley just add some cheeks to your pulley till it is that deep ?What part of the system is the chain coming off?
I think floppy chain is the problem, might take a few more link's out.Other than problems with the chain itself, chain jumping can only be caused by chain alignment issues - whatever their cause at any particular time. This includes "floppy" chain and bumps.
Check the chain angle in each gear to see that it sits easily on the sprocket teeth. If it doesn't, a jump is waiting to happen and may only occur when the drive is under additional strain while going up hill.
If your problem only occurs when using the highest or the lowest gear, it is due to derailleur alignment. By the way, your recent pic or video is only a non-accessible button here.
That can cause other chain tensioning problems, we have used a deeper cut pulley and guide on all our tadpole builds , never had a chain derail, front , middle or back !Wondered about a tention idler between the two also
Have been looking into chain guard'sThat can cause other chain tensioning problems, we have used a deeper cut pulley and guide on all our tadpole builds , never had a chain derail, front , middle or back !
Have also tried chain guide tubes for the first time on the current build .