LISY80 alphanumeric display issue

[Max Power]

I am running a LISY80 board with an 80B alphanumeric display.

The display works correctly if I explicitly write text to it, eg "TEST 1234567890"

If I try to add a variable when setting the text, or if I write the above string to a variable first and then set the display text to that, I get a bunch of garbage on the display.

The display works correctly when emulating the original game code.