I just checked my DCX3510-M PVR this evening (28-Mar-2022) and all my series recordings have re-appeared on the Series tab, including the 4 or 5 new series recordings I created after 28-Feb-2022. I'm going to wait a bit before I re-boot my PVR just in case they disappear again.
I saw your reply and checked my PVR. The series recordings were not there. However, a short time later my PVR stopped working and I had to unplug it to reboot. After the reboot the old and new series recordings were all there.