.Net build fails on lines that do not exist

We have an on-premises TC setup with multiple agents. Recently a significant number of build started to fail with no clear reason. Upon examination of the build log, I can see that it reports compilation errors but the lines indicated do not exist. 

For example:

/xxxxx/ServiceTests.cs(664,17): error CS1503: Argument 2: cannot convert from ‘int?’ to ‘int’

The problem is that this file has only 630 lines and never had more. 

I've made sure that it cleans the directory before each build. 

It pulls the latest code, I've examined the Artifacts and the source zip file, it does contain the latest code. 

I even removed a few tests, to make the file smaller, 589 lines, but it still does report a set of errors on the lines starting from line 664.

Has anyone had anything similar before?