I remember there was a problem with boolean values in JSON::XS a couple of years ago (version 3.01 broke compatibility with JSON). As far as I know, these issues still exist.

The JSON module will use JSON::XS if it is installed, or fall back to the (slower) pure perl JSON::PP if it isn't. If you have a version of JSON::XS higher than 3.01 installed, it may be the root cause of your problem.

The solution I adopted when I had boolean-related problems with JSON in late 2014 was to switch to JSON::MaybeXS and Cpanel::JSON::XS, which are pretty much drop-in replacements for JSON / JSON::XS with boolean compatibility and a couple of other things (including threading) tidied up. Touch wood, I've had no problems since making the change.