The "domains being blocked 0" indicates your gravity list is currently empty. Since there were ads blocked in the past 24 hours, this happened in the last 24 hours. Let's try a few things (easiest first).
Looking at your debug log, your Pi-Hole is blocking domains from your gravity list, so Pi-Hole is reading gravity properly. The problem appears to be in the mismatch between your admin LTE version and your FTL version and the web interface not pulling the data from FTL. You are on an older version of the dev branch (pre- FTLDNS, I think). So, I think the solution is to get FTL onto the current master.
cat /etc/resolv.conf
Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 8.8.8.8
root@linuxserver:/var/log# pihole -up
[i] Checking for updates...
[i] Pi-hole Core: up to date
[i] FTL: update available
Your version of Ubuntu (14.04.5) is unsupported and this may be causing the problem. Have you considered updating to one of the supported versions of Ubuntu (16.04 / 16.10)?
Ah, yes. Updating it is on my list, but since it's working (until now : - ), I didn't see a need to update. Maybe this is the impetus. thanks for your help.
You can also review my topic which was solved coming from an OLD dev build and updated to current master revision
Feel free to post back how you make out
P.S. I just updated to the current version today as well with pihole -up
It took a moment for DNS to kick in once I rebooted the Pi, I hope you have success
Pi-hole Version v4.1.1 Web Interface Version v4.1.1 FTL Version v4.1.2
UP graded to 16.04 last night. Still working out a few kinks in various programs, but everything seems to be working OK. Pihole is working as expected.
It would be night to have some sort of warning on install or run time about using an unsupported OS.