Finally getting around to note some issues encountered, this one involving the module account_tax_cash.
When closing periods, there is a somewhat confusing warning dialog displayed (from code modules/account_tax_cash: c312f17ff3b6 account.py)
I guess I question the utility of this as it’s currently done.
If the issue is that not all payment (or assimilated) moves are included in the invoice, then indeed there is a difficulty in that some payments may in fact not be under payments but over payments, which cannot currently be included in the invoices.
Too, there may be multiple invoices where the payments oscillate between over and under, but do not reconcile [yet] for numerous reasons (such is reality, at times 
).
Without providing much more info such as party, account, moves being considered, this message is rather bothersome if not even a bit worrisome.
In any event, I believe this has less to do with closing the period than with the preparation of tax declarations (for some, it may be sufficient to close certain journals as opposed to the period itself).
Any observations from other users?
Cheers