Dear Maintainer, tried to reconstruct the given backtrace with debug symbols in a gdb session and came to following, maybe it could be of some help. (Still a proper backtrace with dbgsym packages installed would be better.)
Kind regards, Bernhard Reconstructed: #0 0x00007f78b4cfb92f in gnutls_assert_val_int at ../../lib/errors.h:139 from libgnutls.so.30 #1 0x00007f78b4cfdf7c in _gnutls_recv_int at ../../lib/record.c:1773 from libgnutls.so.30 in gnutls_record_recv at ../../lib/record.c:2281 #2 0x00007f78b4e90f38 in gnutls_io_input_read at gnutls_io.c:246 from mod_gnutls.so #3 0x00007f78b4e91ad2 in gnutls_io_input_getline at gnutls_io.c:342 from mod_gnutls.so in mgs_filter_input at gnutls_io.c:595 in ap_get_brigade at util_filter.c:553 #4 0x000055c220cd08e1 in ap_rgetline_core at protocol.c:246 #5 0x000055c220cd336c in read_request_line at protocol.c:682 in ap_read_request at protocol.c:1322 #6 0x000055c220cfe7a8 in ap_process_http_sync_connection at http_core.c:192 #7 0x000055c220cf38b0 in ap_run_process_connection at connection.c:42 in ap_process_connection at connection.c:219 #8 0x00007f78b3bd23df in child_main at prefork.c:615 from mod_mpm_prefork.so #9 0x00007f78b3bd26d4 in make_child at prefork.c:717 from mod_mpm_prefork.so #10 0x00007f78b3bd272f in startup_children at prefork.c:735 from mod_mpm_prefork.so #11 0x00007f78b3bd32f3 in prefork_run at prefork.c:897 from mod_mpm_prefork.so #12 0x000055c220ccc67e in ap_run_mpm at mpm_common.c:94 #13 0x000055c220cc4f57 in main at main.c:819