At Cogneato, we use symlinks to point the web server to different versions of our software for websites. Sometimes, especially on our Ubuntu server, which uses PHP-FPM to serve PHP files through Apache, I was noticing problems caused by scripts being loaded from the previous symlink destination when I changed to the new one. There seems to be some sort of caching going on. The solution was to restart PHP-FPM and Apache after switching the symlinks. On Ubuntu, this looks like:
ln -s /path/to/new-version /path/to/software-link \
&& sudo service php7.2-fpm restart \
&& sudo service apache2 graceful
where the 7.2 is the version of PHP being used. Haven’t noticed the problem since.