EZ Flash Jr keeps rebooting on DMG-01 and GBA-SP. It worked until some weeks ago.

My EZ-Flash Jr cartridge always worked on all three my gameboys:
GBA SP
DMG-01
Gameboy color.

Now it only works on the Gameboy Color and keeps rebooting on the other two units.

I measured the internal battery voltage and it reads 3.03V, which should be fine.
I replaced the battery nevertheless with a new 1220 cell, which reads 3.23V and the behavior is the same!

What can I do? I am running the latest kernel and firmware.

Thanks,