RoP Gold, seems to be a bug with depot battalions:
In the 1741 scenario as Prussians, I have been buying depot battalions to get extra infantry replacements. The units build normally. I receive a message when construction is finished, and the replacements show up on the ledger.
However on the next turn, the replacements just disappear from the ledger. They do not appear to be used and I do not receive a message on what units received replacements.
In RoP (old), I would receive a message on which units received replacements and replacements would only disappear from the ledger as they were used.