Something to check that happened quite a few years ago. We upgraded our firewall and the OSPF routes would 'crash' every 20 minutes with the sort of thing you're seeing.
Problem turned out to be that the firewall default route was the core Aruba-CX switch and the Aruba-CX OSPF default route was the firewall. Due to this - 'unknown' traffic was bounced between the two and every 20 minutes the routing crashed. The fix was removing one of the default routes (on the firewall for us) and this fixed the issue.
At the time neither HPE or the firewall TAC were not much use (each blamed the other manufacturers device). Thankfully a very (now retired) knowledgeable colleague worked it out.
May be something completely different but "just in case" its something to check.