Follow these steps: Go to... Settings, Remotes & Devices, Remotes, Set up a new device, OK, Continue
Now open the battery panel on your remote and hold down the round button just underneath where the batteries are. Hold it until the remote starts flashing green, this will pair your remote to your TV again. These steps fixed my problem of Roku freezing when headphones plugged into the remote.
It's a brand new ultra with rechargeable remote, so no batteries/battery door.
Where is Roku tech support on this? Sort of unbelievable they let something like this hang out there and apparently do not care about this. I mean, it make the earbuds and the remote and the box itself unusable, as it ALL freezes up, has to be unplugged from power, rebooted. Must have done it 10 times (more) in the 1st hour and a half of use.
The solution that worked for me is to open the Roku Remote app on your phone. Plug your headphones into the phone and get sound through the app. THEN go back to your actual Roku remote and the problem will be fixed. Until it happens again.