I would NOT say it's a common thing,but S%#t happens! A mold MAY cast to big,or a batch of checks gets thru QC a bit small.etc.
I have a BUNCH of molds and use a variety of alloys,some are more compatible than others. When I use linotype alloy I get fat bases MOST of the time. The feeler makes it easier to seat the checks. Even when using a "push thru" die like a Lee, you can get checks squashed on one side or the other.