I reproduced this. Powered Belts replaces the belt entity during power changes, while Belt Overflow keeps its reference to the old, destroyed entity.
A possible fix in Belt Overflow is to remember each tracked belt’s surface and position. When its reference becomes invalid, its existing processing loop could find the replacement there, update the reference and recalculate overflow behavior - or remove the entry if the belt is gone.
That should fix this particular failure without full-map rescans. An event-based integration would need changes in both mods, since power swaps aren’t announced and Belt Overflow doesn’t currently listen for script-built replacements. I’m leaving the combination unsupported rather than adding workarounds (i.e. Belt Overflow world-refresh).
