[GNC] Gnucash crashes after upgrade

[gnucash3 at skewray.com]

A year or two ago I was running Ubuntu 16.10. When I upgraded to the next
Ubuntu version, Gnucash did some moving and reformatting of my config files.
When I ran Gnucash, it would hang up inside any register and crash.  I 'solved'
the problem by running 2.6.12 in Virtualbox on Ubuntu 16.04, which is what I've
been doing ever since.  Ubuntu has upgraded a few times, and the issue
persists.  The current version that still doesn't work is Gnucash 3.4.

Is this a known issue? Is ther a previous thread in this list that addresses
this?  If not, how would I go about starting to debug the issue?

Places where config files seem to be:
    .config/gnucash
    .gconf/apps/gnucash
    .gnucash/books/Gnucash
    .local/share/gnucash/books
I don't know which of these is from before the conversion and which are new.
The problem might also be in a library, I guess.