Apache is restarting from time to time (no replies)

Apache is restarting from time to time after an error:

[mpm_winnt:notice] [pid 1496:tid 348] AH00354: Child: Starting 64 worker threads.
Assertion failed: ((((rwlock_t *)*rwl)->valid == LIFE_RWLOCK) && (((rwlock_t *)*rwl)->busy > 0)), file /home_hdd_4/charlie/mxe_clone/tmp-gcc-i686-w64-mingw32.static/gcc-5.5.0.build_/mingw-w64-v5.0.3/mingw-w64-libraries/winpthreads/src/rwlock.c, line 40

What can cause that error?

Apache is the latest version : Apache httpd 2.4.39 - from WAMP server 3.1.9 32 bit.