All forces returned but cannot do PS. Only SS shows as an option

You only get 2 PS per 24 hours, regardless of brigade status. So at 00:00 game time you can PS again.

yeah it showed my brigades returned. I hadn't encountered that before.

The brigades doesn't matter - you can even have 4 brigades out. Or your brigades might be out and back before the 00:00 Gametime reset.

Go to "Main Menu" and look at "PS Left".

It's because PS return time was changed from 23 hours to 18 hours to make things more convenient.