Attempting to reparse posts or everything using the CLI and a PHP version less than 5.5.38 (which I tested it's true) throws an error and "de facto" denies the reparser to run.

Parse eror: syntax error, unexpected '[' in /home/www/...forum/bin/phpbbcli.php on line 76

Ref.: former fix.. https://github.com/phpbb/phpbb/commit/b5e850b6df703a97f654f92cea9143754c3086b8

support issue:

https://www.phpbb.com/customise/db/extension/mathjax_2/support/topic/193236?p=639351#p639351

and the follower.

I have the new fix ready, I will push it soon.