> today there is only one file in the stats subdirectory: dirreq-stats.
> Is that normal?
I think so, yes. I just checked a healthy relay:
$ sudo ls -l /var/lib/tor/stats
-rw------- 1 debian-tor debian-tor 1412 Feb 17 22:39 dirreq-stats
-rw------- 1 debian-tor debian-tor 185 Feb 17 22:39 hidserv-stats
The second file probably only appears if your relay has the HSDir flag and is acting as a hidden services directory.