Try to do idml again.
Or ask here (download to some dropbox/yadisk and give it the link).
In most cases idml helps! Instead CS3 and below - needs to do .inx
You will have to either identify the plug-in and find out if it is available and install it on the coworkers' machine(s) or have the person who created the original file resave the document with that plug-in disabled (depending on the plug-in this may alter part of the document). An IDML of a document that requires a certain plug-in will not usually do away with that document's need for the plug-in.
I have over 3,000 indd files effected by a now missing element of a 30 day Xmpie plugin that was an eval copy and expired long ago. Seems the pluin went in with ID2018 -I am using ID2020. I have no idea why the problem just poppped up now - BUT am thourly hooped. Any suggestions? (please & ty)
I'm not sure I understand why you would use a plug-in that you only had a thirty day license for to create that many documents or how you could create that many files in just thirty days. But the answer I gave over a year ago is still the best advice. Find an updated version of the plug-in and buy it legitimately.