At least since the v6.15-2-99 update, I am noticing that my custom DNS settings pointed to NextDNS are failing as indicated by the NextDNS dashboard, logged traffic against NextDNS and confirmed by viewing DNS results via dnscheck.tools.  In fact, dnscheck.tools seemed to show my DNS resolved changing over time from OpenDNS, to Google and back without changes on my end.

At first I thought it was the NextDNS service but found it was working fine, if I toggled my phone off of wifi while still using my NextDNS app.

I decided to revert the DNS settings to IP assigned and then back to Custom DNS via two reboots and this seemed to fix the problem for a time.  Yesterday again I noticed differences (items not filtered/blocked) and check the NextDNS logs.  Custom DNS settings appear to have stopped four days earlier.  Again a reboot through 24 hours seems to have 'resolved' the issue.

Is anyone else seeing this and/or is it a known bug?  It has not previously been an issue.