With mediawiki 1.35 there is some clash with the way this extension registers itself with other extensions like Maps. I have rewritten it to use extension.json and a new Hook approach. See https://github.com/jrbray1/SimpleTable where you will need extension.json and SimpleTable.php, and add to LocalSettings.php
wfLoadExtension( 'SimpleTable' );
I don't understand php or mediawiki internals, so the solution is fragile