There are few developers complaining and having issues (when you consider how many developers are actually on itch.io). The complaints are all variations of the same theme:
1. Developers want to upload extra-large files and can't (I have no idea if players even download these)
2. Developers want to get paid more promptly (but itch.io has to deal with fraud, so they're careful and that takes time) followed by accusing itch.io of withholding money because the developers haven't read the documentation. Itch.io is free, you can give them a share if you want to (and you should), but they pass on the charges by the payment processors to the developers - developers often struggle to understand this.
3. Developers complain that nobody can find their games / their games are not indexed (that is difficult - you basically need to promote your game elsewhere (social media) because the chances of it being seen here is potluck - some games win the lottery and get featured, most games don't).