WordPress Automatically Removing Script – Sometimes

I have an issue where occasionally wordpress seems to modify a page to remove a small script. This starting happening around last November, and occurs infrequently, but when it does, it happens several times on the same page. After a few cycles of reinserting the script (and having it deleted), it seems to stick around. This isn’t a case of switching back and forth with text/visual view either – which is the only other reference I can find online. Its there working fine, then with nobody in the backend, the script just disappears.

I can view side by side revisions, it registers whatever user put the script in, then the next revision it will be missing and there is no user associated with the removal.

The script is just a link to an external site which build a booking widget to integrate with our sales software. We appear to be the only ones with issues.

Any help or suggestions would be much appreciated.