we stopped swaddling our baby boy after 1 week. he hates to be swaddle and always struggle to get out. Only occasionally when he is tired, he is fine with the swaddle as he will fall asleep faster than he manage to find his way out (crying for us to get him out).
I stop swaddling at about 2 months though there will be times my second born will be startled during sleep. Reason is the same as you, she likes to wriggle out of the muslin. Sometimes I will change to velcro type swaddle or the zip type.
I stopped after week 1 as well. We made a mini pillow filled with green beans and put it on bb’s abdomen. It helps to relieve baby and doesn’t get startled as easily as before.
My baby hates to be swaddled so we stop after a week. Now i change to velcro type and yes it’s normal to get startled, it will get better in time