I don’t think you are crazy…
My Garmin 620 has not failed me very often but when it has failed me it has failed me pretty bad.
10k race (3 identical laps) in May 2013 with 910XT : link .
Now SAME 10k race with SAME 3 identical laps in May 2014 with FR620 : link . Look like I was running in very different streets each lap, pace was wrong, distance of course was wrong but the map really is the funniest part 
. Now to its defense, it was raining pretty bad during the race this year…
Having shown that, it seems with the latest firmware for FR620 and the latest GPS tracking firmware (both get updates every now and then) I haven’t had this happening lately and I’m one of the lucky one who did not have his FR620 crashing during runs after latest firmware installation.
So I’ve not been the happiest FR620 custommer in the world and I do trust my 910XT more but since the FR620 keeps improving update after update and since it is so light and comfy on the wrist, I decided to keep using it and I’m sure at some point it will be 100% reliable just like 910XT !
Hope this helps…