If you hit = and expect to see line numbers, but only see byte counts, then line numbers are turned off. Hit -n to turn them on, and make sure $LESS doesn't include 'n'.
Turning off line numbers by default (for example, setting LESS=n) speeds up searches in very large files. It is handy if you frequently search through big files, but don't usually care which line you're on.
I typically run with LESS=RSXin (escape codes enabled, long lines chopped, don't clear the screen on exit, ignore case on all lower case searches, and no line number counting by default) and only use -n or -S from inside less as needed.