New holsters? If so, new holsters require a "break in" period just like a new pistol. Drawing from the holster will loosen it up. Practice drawing (unloaded weapon; of course) regularly. This will break in the holster AND get you familiar with the different characteristics of the holster.
I have a Galco 'Fletch High Ride' belt holster for my Kimber and was told when I bought it that the thumb strap would be tight. What was recommended to me, and advice that I followed, was to take some rubbing alcohol and apply it to the inside of the strap. Just enough to get the strap damp so it could stretch enough to fasten with the gun in the holster. After applying the alcohol I placed the unloaded gun into the holster with the hammer cocked back, fastened the strap, and let it dry in place. Fits like a glove now, no problems fastening the strap and no damage that I have been able to see from the alcohol.
Well... I would take a sharp razor, or knife, and CUT IT OFF! The strap is unnecessary unless required by some department policy for LEO's, if the holster is well designed.
20-30 years ago, most every holster came with a strap, and we were stuck with them. I moved away from straps years ago... They get in the way. Most don't allow for one-handed re-holstering, and in many cases, the snap provides a false sense of security.
Many who get holsters with a thumb break feel the need to prevent the cocked hammer from failing, and falling on a live round.
Sadly, the misinformed fail to realize what is actually required for the hammer to fall on a 1911... At least one that has been verified for safe operation.
The thumb safety would have to be off, the grip safety depressed, and the trigger pulled (on a S80). FWIW, the thumb strap would not prevent the Firing Pin from moving if enough enertia occurred to get it moving toward a primer.
Out in the field, on horseback, or maybe an ATV, I could see a reason for having one, but for most people, I see no real value, and again, with a properly designed holster, they are not necessary.
Lastly, I'm betting that you tried to snap over the uncocked hammer, although a new, un-broke-in holster could be tighter than normal.