Version above 1.2.6 not compatible with WordPress version

Hi there. I use the Expound theme, and GetYour Guide worked perfect for me. When I upgraded to WordPress 5.6.1, though, my website malfunctioned.

After hours of troubleshooting, I found it was the GetYourGuide plugin that made my site malfunction. A manual downgrade to plugin version 1.2.6 proved to work – both for my website AND the plugin.