Found an overflow error...

[Elessar2]

No surprise given my huge orders of battle, but I'll outline the figures in question here:

Russians have 127 base builds for unit slot [03] (the 4th one since they start with [00] for HQs), the maximum allowed in the editor. This is amenable to increases from the Army Mobilization tech slot 17, 10 per level, and Russian had gained 1 level in that tech at the time.

She had 13 remaining builds allowed out of 137. When I bought the 4th unit, the counter overflowed from 10 to 265 (256 +9).

Seems like an easy fix, unless there are deeper associated limits in the base code.

[Hubert Cater]

Looks like you reached the data size limit of 256, which is the limit size of the integer used to store the build limit values.