The site that I saw had a bunch of those Post Custom Fields that had a bunch of strings that had been encoded a bunch of times so that they were unusable.
Some solutions, in order of complexity
- stop using the plugin (and perhaps switch to the new up votes)
- delete all of them
- delete the bad ones
- edit those fields to make the data back into valid json strings.
The site that I saw had bad data that was years old. This appears to be a bug that existed years ago that is only now being discovered.
It might be possible to write code to fix the broken json strings, but I wasn’t able to see how to do that in 10 minutes.
See Question Answer Plugin - #301 by pfaffman for examples