Hello,
recently we upgraded from 5.1 to 5.2 few servers (CentOS7 and Raspbian) and all seems to be working fine, but I can see on (yes I know, not recommend and supported) rasbian issue with metrics and in the log I can issue this error:
Nov 13 10:21:33 dns-cache-2 kresd[15232]: map() error while connecting to control socket /run/knot-resolver/control/H#003: socket:connect: No such file or directory (ignoring this socket)
Nov 13 10:21:33 dns-cache-2 kresd[15232]: map() error while connecting to control socket /run/knot-resolver/control/H: socket:connect: No such file or directory (ignoring this socket)
Nov 13 10:21:33 dns-cache-2 kresd[15232]: map() error while connecting to control socket /run/knot-resolver/control/: socket:connect: Connection refused (ignoring this socket)

the error is triggered  by opening "ip:8453/metrics" and it show almost empty response:
# TYPE resolver_latency histogram
resolver_latency_count 0.000000
resolver_latency_sum 0.000000

root@dns-cache-2:/# apt -qq list knot* --installed
knot-resolver-module-http/unknown,now 5.2.0-1 all [installed]
knot-resolver-release/unknown,now 1.7-1 all [installed]
knot-resolver/unknown,now 5.2.0-1 armhf [installed]
root@dns-cache-2:/#
root@dns-cache-2:/# uname -a
Linux dns-cache-2 4.19.97-v7l+ #1294 SMP Thu Jan 30 13:21:14 GMT 2020 armv7l GNU/Linux


Could it be a bug or something related to mix armv7l and armhf? I know of the limitation as we discussed this setup on raspberry some time ago. I just want to share my experience as it can be useful and if you will have any tip I will appreciate it.