Thank you for your detailed answer.

The comment from @moecki brought some light into the darkness, api.steemit.com generates the errors, RPC's such as api.moecki.online or api.worldofxpilar.com return the correct data.

So, the RPC api.steemit.com needs to be fixed.

In addition, it would be desirable, that the RPC setting is possible in the user settings. This would require updating the selection of RPC's, the current selection contains non-functioning nodes.

I sincerely hope that now that the cause has been clarified, someone will be able to correct it. May your mentions be heard. I have written a comment to @steemchiller, hopefully he can say something new about the current status.