This exactly matches the time when my 22 outbound connections across multiple nodes to bitprojects (Many connections to bitproject.io nodes?) dropped.
Likely, all nodes on the network connected to bitprojects lost their outbound connections to bitprojects at the same time and all of them started looking for new outbounds at the same time.
This matches with the post from @bitprojects in Many connections to bitproject.io nodes? - #24 by bitprojects.
I guess this solves it.