Very slow startup time suddently, why?

This drives me crazy! It happened now a few times where I modify my program, for example by adding code, or linking more libraries, and suddenly the startup time of my program goes from 0.1s to 2s!
The program is just a command-line tool, and if I run it with --help it just displays the possible options
and exit. But suddently, it now takes 2s.

I was using ocaml 4.09.1, and it seems to work better in 4.11.2.
Still very weird that simple changes in 4.09.1 suddently change dramatically the startup time.

If you are on macOS this could be an issue.

Nope, on Linux.
Also bonus question, why there is no more backtrace in 4.11.2?
Now when I get an exception instead of precise location I get:

Uncaught exception:
  
  Parse_mini_rule.InvalidPatternException("no-id", "foo$", "ocaml", "Parsing.Parse_error")

Called from unknown location
Called from unknown location
Called from unknown location
Called from unknown location
Called from unknown location
Called from unknown location
Called from unknown location

This used to work perfectly fine in 4.09.1

Without more context, and even better a reproduction case, it is hard to guess what is happening.