This application has been live for many years and the persistent corruption issue started a couple weeks ago.
...Access databases are not intended for multi-user access...This is simply not true, so don't worry about it in the least. Like many other people here, I've been developing multi-user Access databases for 2 decades now without issue. It all comes down to knowing what you are doing. Every multi-user database must be split and each user given their own copy of the FE to run locally.... If ever you wish to learn more regarding properly setting up multi-user Access databases see Setting Up an MS Access Database
How big is this database? Not in size but in records.