That's a crash in OpenSSL (which version was updated to v1.1.1k in Cool VL Viewer v1.28.2.23)...
And nothing wrong in the viewer code to explain it !
I'm afraid it's an OpenSSL (or possibly libcurl, since it is what calls OpenSSL in the stack trace) bug.
I'm also seeing occurrences of rainbow textures detection in your log with the activation of my work-around ("Temporarily disabling HTTP pipelining"), which is sort of a surprise to me since despite intensive stress-testing in SL, I could not get them to happen with the new libcurl (but they still do happen in OpenSim, at least on OS grid).
Perhaps you should try and recompile the viewer with 'set(USE_NEW_LIBCURL OFF)' in indra/cmake/00-BuildOptions.cmake...
EDIT: just noticed that to rebuild successfully with curl v7.47, you need to fix a bug I introduced when I added support for libcurl v7.64.1: line 164 of indra/newview/llappcorehttp.cpp change:
to read: