Cache entries not created for some expr and modules

Steps to reproduce (on system with new stats and HPCC-19684 merged):

1) Expand an archive from the private regression suite:

eclcc leaks.eclxml --expand XX

2) Delete the local cache

3) Run eclcc a first time

eclcc -syntax -main IdentityManagement_Services.ReportService --nostdinc -I XX -legacy --timings --internalextrastats --ignoreunknownimport

4) Run eclcc a second time

eclcc -syntax -main IdentityManagement_Services.ReportService --nostdinc -I XX -legacy --timings --internalextrastats --ignoreunknownimport --tracecache

Not all of the simplified entries are used, and many of the cache items are marked as out of date.  Why?