See pic and Layout file. Size A0 paper. Using default text in layout. When rotating the text 90 degrees, some parts of the first letter are cut - it depends on the position on the paper.
I can reproduce it. This appears to be related to the distance from the page’s origin (top left corner) to the text. On large sheets text on the far right and/or bottom get this cropping worst.
We have seen this before, but we haven’t had time to determine the root cause of this issue. As @DaveR said, it gets worse the further from the page origin you get.