Resurrecting a problem that was supposedly "solved" a couple of years ago, can't prove it by me...
I recently purchased a Roku Voice Remote Pro 2 as a recommended replacement for a misplaced controller. This model paired and worked properly for a couple of weeks until the other day. I have gone through all recommended troubleshooting and resolution procedures with no success. Chatted with Customer Support earlier today, who opined this latest & greatest model was NOT compatible with my Roku Express unit although, as previously mentioned, it worked wonderfully for a while.
My Roku Express is a Model 3900X, software version 14.1, running on a Samsung 60" TV. There are no other components hooked up to the TV or Roku Express. The Support Rep told me, because of the "incompatibility" issue, I needed to by the "Basic" Remote unit to replace my newly purchased latest version controller... forgive my skepticism. When all is said and done, has ANYONE at Roku, or anywhere for that matter, diagnosed the problem & designed a working solution?? One would think that after 4+ years, a lightbulb would have come on in SOMEONE'S head!?!
I believe the Express 3900 only uses an IR remote/receiver, therefore the Voice Remotes would not actually "pair" to them. You would just point the remote directly at the device (line of sight).
I see no reason why the Voice Remote Pro v2 would not be compatible in IR mode, and you likely ended up chatting with a Roku representative that does not understand the devices.
---
As for the volume button not working, the Power and Volume keys are programmed to the TV. Therefore, you may just to set it up again with the Samsung TV (through the Roku device settings) to get it working properly again. It is likely just having an issue with the stored codes.
Some users are having an issue when they are using the samsung remote when it is set to "universal remote" in the TV settings and having undesired behaviors on their Roku device. Perhaps the reverse is true when trying to use the Roku remote with the Samsung TV. Try going into the Samsung settings (using Samsung remote or the TV buttons if applicable to navigate, not Roku remote) and disabling the "universal remote" setting if currently enabled.
When you set up the remote to control the TV, did you use the IR or CEC setup? If IR, I've had the remote stop transmitting (verified by looking at the remote through a digital camera), but I haven't seen that happen in a while. If CEC, sometimes you have to reset things by removing and inserting the HDMI cable and/or unplugging the power from the TV and Roku device briefly.
I wouldn't pay any attention to what the support person told you. It always makes me wonder why people are so desperate to reach a human when answers like that are given.