bash reverse search not working

Ctrl+R not always working. Suspected for a while. Verified today. Because I knew what I was searching for was there.

cat .bash_history | grep searchterm
bill@bill-MS-7B79:~$ 
(failed reverse-i-search)`trim': yyf X-Plane 11 King Air C90 autopilot tips and Tricks

The following produced many results
bill@bill-MS-7B79:~$ cat .bash_history | grep trim