Hi!
Thanks for your post and sorry for the trouble!
This is indeed caused by the tables being shown in tabs:
When tables are shown in tabs or accordions, or similar, they are initially hidden (when the page is loaded). And hidden tables don’t have a column width, so that certain calculations can’t be performed (like for example how the header row should look like or when columns need to be collapsed).
Now, very often it is possible to make this work by adding a “Custom Command” with some custom JavaScript code, which basically re-triggers these calculations once a tab is switched. However, as that code highly depends on the site in question, with its theme, etc. playing a big role, I can only offer looking into that more deeply for holders of a TablePress Premium license, which are then eligible for direct email support. The premium versions also bring more possible modes for making tables responsive in the Responsive Tables feature module, which, for your tables, might even be better than the Collapse mode.
Regards,
Tobias
ok, that’s what I suspected. Thanks for confirming.