That is because of a change to how those warnings are handled in WeBWorK 2.18. Prior to 2.18, those message were only in the apache2 error log as you saw, which is not a place that a problem author making a mistake in authoring a problem will ever see. So in 2.18 that was changed, and those messages are now shown for instructors. The point is to make problem authors aware of their mistakes so they start fixing them.
WeBWorK Problems
Some questions are not loading parserUtils.pl
This forum has a limit to the number of forum postings you can make in a given time period - this is currently set at 10 posting(s) in 1 day