Then unplug all HDMI connections, then the power connection. Wait at least two or more minutes and do not connect HDMI. Try the volume up and down now. If that works I wonder if the TV was under some HDMI CeC (control.)
If that fails, remembering to not plug in anything other than power I'd try all the resets noted in their online manual.
Some note to "power cycle the remote" which is to remove the batteries and hold the remote power button for 5 seconds, release and wait a minute pop the batteries in and test.
More ideas at https://www.google.com/search?q=e32-c1+volume+stuck&gl=US
https://www.wikihow.com/Reset-a-Vizio-Remote covers another type of remote reset worth a try.
We have four 3 year old Vizio TVs, 2 e32-c1 (table top) models and 2 e50-c1 (wall hung) models. All work fine as far as picture, etc, but one of the e32s has an issue where we cannot adjust the volume at all via the remote. We are on AT&T U-Verse, and all 4 cable remotes work fine on all the sets for changing the channel, but none work on this one e32 at all as far as the sound adjustment is concerned. It's not battery, as its remote works normally on the other sets.
We've tried all 8 remotes on this one TV's sound, but they don't work on it at all, despite working uneventfully on the others. Luckily the problem set does have sound, so it's usable, we just can't turn it up or down. I contacted Vizio support who said it appeared to be "repairable", but we'd need to have an outside tech come to look at it, which of course would be pricey.
What could cause this? We understand it's out of warranty, but is there a fix? We are starting to think it would be cheaper to just wait for a nice sale and get a new one