I can update the Metabox plugins one by one. When i click the next Meta Box plugin the error above is showing. Then i refresh the browser, the update button disappears. I have to refresh the browser again to get the update button back and succesfull update the plugin. This repeats itself (see video).
Sorry for hijacking but I came here because we have the same issue. But also the updater almost never shows available updates for us. Like now the Group extension is at 1.0.5 but it doesnt show that 1.0.6. is available.