It just came to me this morning that I haven't tried to specify a different path in a source to check if it will successfully test the csv file. Tried it a while ago and figured that the problem is isolated in the folder we usually put the csv files. I totally forgot that I have shared that folder for easy access and limited it to mea and several others. I added 'Everyone' with read-only access and voila, all sources are working again! 
Thanks!