hudson.plugins.git.GitSCM.xml
the line
<generation>10</generation>
got changed to
<generation>31</generation>

• sorry no idea how
  results were git repository symbolic links got converted to files.

1. GOOD - <generation>10</generation>
   ls -l subdir/mylink
   lrwxrwxrwx. 1 jenkins jenkins 5 Mar 26 16:56 mylink -> ../..

1. BROKEN - <generation>31</generation>
   ls -l subdir/mylink
   rw-rw-r-. 1 jenkins jenkins 5 Mar 26 16:56 mylink

This worked w/o updates or plugin installs 2 days ago, had to be changed by some configuration change action - Like testing JGit then changing back go Git in system config.