[GNC] Gnucash 3.3 suddenly crashing on Ubuntu

[Colin Law]

I have been using version 3.3 installed from the Ubuntu repository on
Ubuntu 18.10 for some weeks.  Suddenly today it will not open.
When I run it from the command line I see the output below.
The gnucash trace file is empty.
Googling found similar problems during build and suggested renaming
~/.cache/guile but that did not help.
I have another machine running the same version of ubuntu and gnucash
and it continues to run ok, however it is behind on system updates so
it is conceivable that an upgrade to something else has caused the the
problem.  I am not going to update that machine at the moment in case
it stops working there too.
I have not knowingly made any changes to the system since it last ran.

Hopefully someone will have some suggestions.

Colin

~$ gnucash
Backtrace:
In ice-9/boot-9.scm:
  2994:20 19 (_)
   2312:4 18 (save-module-excursion _)
  3014:26 17 (_)
In unknown file:
          16 (primitive-load-path "gnucash/utilities" #<procedure 56…>)
In utilities.scm:
     28:0 15 (_)
In ice-9/boot-9.scm:
  3377:20 14 (process-use-modules _)
   222:17 13 (map1 (((gnucash core-utils))))
  3378:31 12 (_ ((gnucash core-utils)))
  2800:17 11 (resolve-interface (gnucash core-utils) #:select _ # _ # …)
In ice-9/threads.scm:
    390:8 10 (_ _)
In ice-9/boot-9.scm:
  2726:13  9 (_)
In ice-9/threads.scm:
    390:8  8 (_ _)
In ice-9/boot-9.scm:
  2994:20  7 (_)
   2312:4  6 (save-module-excursion _)
  3014:26  5 (_)
In unknown file:
           4 (primitive-load-path "gnucash/core-utils" #<procedure 5…>)
In core-utils.scm:
     40:0  3 (_)
In ice-9/boot-9.scm:
  2071:24  2 (call-with-deferred-observers #<procedure 7f094403d2b8 …>)
   260:13  1 (for-each #<procedure 562dd5c018e0 at ice-9/boot-9.scm…> …)
In unknown file:
           0 (scm-error misc-error #f "~A ~S" ("Undefined variab…" …) …)

ERROR: In procedure scm-error:
Undefined variable: gnc-build-userdata-path