Would guess that you have a broken key bolt on the carrier, that is causing the gas leak (rotate another carrier into play to confirm such), with the gas leak at the carrier key to top of carrier.

Or,

Gas block at the barrel became loose, and the gas leak is between the block passage to barrel gas port exit, if you don't have a rupture in the gas tube causing the leak instead.

And/or the one that really sucks to get out,
you had a blown primer piece find it way into the front of the carrier key channel, the gas tube loves to pack it deep to really make getting it of the channel that it just blocked a PITA instead.

With the key metal peen into the sides of the key bolt spines, it hard to tell when a key bolt snaps, since the peen metal will hold the head in place in the key.

Same with gas block bolts coming loose, since it can either create a gas leak between the block and barrel, or block can shift/rotate to block the two passages instead.

So easy way to check on the key, hold the bolt inwards, CLP around the entire base of key to carrier top, and pressurize the front of the key with 100lbs of compressed air to look for leaks. The bottom of key to top of carrier should have no leaks, while it will be normal for some air to leak out around the tail of the bolt to gas passage channel in the carrier.

On gas block, piece of rubber tubing on end of gas tube inside the receiver, CLP around the front and back of block to barrel, and pressurize the tube with 100lbs of compressed air. If passage to port is still correct, will get air flow out the barrel gas port to bore, but since the gas port is small enough, plenty of back pressure to check for leaks of the block front and back to the barrel.

If leaks are found, then either needs to be pulled so the fouling between the two can be cleaned, then key reinstalled with new Bolts, or in the case of the gas block once correctly aligned, it's set screws tightened with 272 loctite used to keep them from backing off again.