I am afraid this did not work. I tried this before posting the issue. Thank you for your response, however.

Michael Spaventa 

Could be you solved this already, but just in case!!

The error points towards the Term Verifier attempting to access a term that does not exist in the "collection".  The most likely reasons for this are that your termbase is missing terms, or even that your termbase is stored on a OneDrive path, or some other cloud solution.  The reason this unlikely sounding reason is a potential culprit is that your termbase file (.sdltb) or project files (.sdlproj, .sdlxliff, etc.) are not fully synced when accessed by Trados Studio, and partial data could result in unexpected behaviour like missing entries or incomplete content.

Worth a check if this is still causing you a problem.

Michael Spaventa 

Could be you solved this already, but just in case!!

The error points towards the Term Verifier attempting to access a term that does not exist in the "collection".  The most likely reasons for this are that your termbase is missing terms, or even that your termbase is stored on a OneDrive path, or some other cloud solution.  The reason this unlikely sounding reason is a potential culprit is that your termbase file (.sdltb) or project files (.sdlproj, .sdlxliff, etc.) are not fully synced when accessed by Trados Studio, and partial data could result in unexpected behaviour like missing entries or incomplete content.

Worth a check if this is still causing you a problem.