Why Would Invisalign Attachments Fall off or Break?

It is not unusual that there may be a couple of teeth that, because of the bite, are hitting hard on the opposing teeth where the attachments are. Attachments are placed on teeth that require the most movement, so these teeth are put under the most stress. Lastly, if the teeth got contaminated during the bonding process (from saliva in the mouth), it could affect the bond of the attachment to the tooth. You should call your dentist and get right back in as soon as possible to have these re-bonded and checked.
You will find that there will be trays that feel loose quite early after placement and others that will only start to feel loose at the very end of the 2 weeks. It all depends on which teeth are moving at each stage. Regardless, wear your tray for the 2 week minimum, unless your dentist advises otherwise.

If attachments repeatedly come off of the same teeth, rebounding is a challenge. The tooth surface NOW is not the same as day 1, so alternatives may need to be explored.