Comment 42 for bug 1974214

About line 3781 in src/tls-gnu.c there is a call to
gnutls_certificate_free_credentials().

Please test with that commented out. I think that is freeing the shared
CA-bundle, which we then try to re-use in the second connection within
the same process. That would account for the with-preload crash, and
perhaps for the without-preload also.