[Plugin: FeedWordPress] Error Incorrect string value

I’m getting a lot of these errors in my php-errors logfile, and the file was huge (900 MB). However the feeds are working, and everything seems ok. I read somewhere that this has something to do with character sets, but in my case all systems are using UTF8.

Any ideas what to do to get rid of the errors? The errors seem to appear when a feed is updated.

Here is one line from the log:

[Log entry moderated. Please use the pastebin]

https://www.ads-software.com/extend/plugins/feedwordpress/