Most likely the threaded insert in the ball head has been pushed inward or shifted, so the tripod’s mounting screw can no longer engage correctly. That matches the reported fix here: once the thread in the head was found to have been pushed inside, the problem made sense.

There usually isn’t a normal “setting” on a ball head that changes the mounting fit, so this is more likely a mechanical issue than user error. Carefully inspect the threaded socket on the underside of the head and compare its depth/position to how it looked before. If the insert has moved, it may need to be reseated.

A temperature change causing expansion/contraction is theoretically possible, but it’s a much less likely explanation for a tripod head suddenly not threading back on.