Phonoland

WB0H WB4H : no song played.
WB3 or : can play only the first 100 songs, make sense as code is for 100 selections.
WB4 : all selections played

I assume the motor of the wallbox is already in 50Hz, as it's for french market.

I still get the same symptom : "sometimes the new selection stop the playing song".

This Rock-ola 503 is a 160 selections.

I thought it was a bit of a long shot, the Hz value might be printed on the plate at the back.Did you try the adapter test, its detailed in the manual.
I had problems with a previous adapter and was told on rare occasions that there can be interference with the cancel lead and button, also i hooked up another one with a small amp in it and on a random basis it would cancel songs so i don't use the amp inside it any more.
Also i had another wallbox and i had a treadmill plugged into the same ring circuit , if the wallbox was operating at the same time as the treadmill it would cause a song to be canceled, i discovered afterwards the treadmill motor was on its way out and somehow it affected the adapter
regards
clones