I've been dealing with issue since I bought my Roku Ultra in November. No issues with two other Roku Stick + devices same apps. Changed to Pandora Beta. On occasion it might play several bits and then randomly will just halt at the end of 4 minute bit and stop. Sometimes, if you wait 30 sec to a minute, it will switch to the next bit. Sometimes it will kick out of Pandora to the main Roku home page. Sometimes an Error message will appear and it will start playing anyway. This happens almost every time we use the Beta version. I've power cycled it at least a few times in January. No change. I also have Pandora on my Visio TV and it never has a problem.
I haven't gone back to trying the non Beta one again. 4670x model number.