Also chiming in here having the same issue for almost 2 weeks now. A HT-J4550 model and tried all the reset methods, even a forced USB firmware update, still stuck in a boot loop.
It be interesting to see a fix as the model is 4 years old, 5 months old. Unfortunately I held the idea that once the machine goes I'm upgrading to 4K, but it be handy for another household I have in mind for this if the 'security certificate' can be updated if it is the issue as reported. There's a lot of life left in the speakers, given that it is in use every single day since purchase.
On Samsung's Product Page, there's a Firmware File on there. Placing that on an empty USB, unfortunately my model does not have a selectable function USB channel, it has to go through the Settings page. Because of the boot loop, I can't reach the settings page long enough before it restarts.
Same issue with a BD-JM57. Worked fine a week ago, then it just started cycling. I'll barely have enough time to get a directive in from the remote while it's cycling since the home screen only flashes for around 2 seconds. I've had it unplugged since around Thursday.
I'm in the UK. BD-J5700 started doing this on 21/6, was OK day before. My HT-C6930W home cinema system is fine so far. I also have another Samsung BD player stashed but I ain't turning it on.
We got our disk out by flipping unit over. On underside there is a arch opening. If you stick a small screwdriver in there you can turn the wheel under the cover. This drives the tray. It takes a quite a few turns, but our disc came out. I do not know which way we turned the wheel, I was so mad I paid little attention to the finer details. Good luck.
