I don't have that file on my system, pihole-FTL says:
Feb 1 11:24:24 dnsmasq[29598]: failed to load names from /etc/pihole/custom.list: No such file or directory
I assume this entry has a purpose, but the file isn't created until you make the first entry. How (pihole command OR web interface) are entries added to this file?
SORRY. didn't see it until your screenshot, must be getting old...
Unfortunately, the file (web interfae) doesn't allow the full hosts file specification, e.g. multiple names for one IP on the same line, such as (example).