Yes, I've had the same problem for months unfortunately with any version of v20 that I've been using.
Sometimes it will work flawlessly, sometimes it won't scrobble a single track. Rebooting my PC normally fixes the issue for a while so I'm guessing something is interfering with the scrobbling sometimes.
Even during the times it won't scrobble it will still show the song as playing now on lastfm website but at the end of the song JRiver doesn't seem to send a confirmation that the song has ended so it doesn't get scrobbled and added to my stats.
I can still force scrobble a song by playing a couple of seconds near the end of a song then double clicking the next song in my queue to skip forward. I have to constantly be checking if each song has scrobbled and forcing the ones that don't which is an annoying waste of time.
Other times it can be scrobbling perfectly but as soon as I click to fast forward part of a song from then on it won't scrobble any songs any more which is strange and have to reboot again.
I never have any issues scrobbling from Spotify so it may not be a lastfm problem but something to do with JRiver not confirming the song has ended.
I have my JRiver set to pass my audio to my USB DAC via WASAPI, which Spotify cannot do so may be something related to that? I never used to have a problem with scrobbling from JRiver until the last few months though and my audio setup hasn't changed.
My submission filter is still set to default: Scrobble only audio, artists is not any empty, name is not empty.
Any ideas how to fix as this is driving me mad! I'm very OCD about my scrobbles