If the shortcuts have any commands for locks or garage openers, they are blocked. That is why some of mine are missing, anyway.
You are correct. I checked the missing shortcuts yesterday and found that they all contained an "Unlock" command. Removed 'unlock' from 1 and it immediately showed in the drop down list. You can use shortcuts with 'Lock', but not 'unlock'. Apparently IFTTT blocks 'unlock' for security reasons.