[Plugins in general] Updates don't work

Since 2015 my wordpress-plugins do not upgrade from the menu any more. None of them. When I click to update, wordpress just hangs and no progress is made. No error message, no blank screen, nothing. Regardless of whether I pick the updates individually or try to upgrade them all together.

I checked folder permissions and cranked them up to 775 for folders and 740 for files. Still no improvement.

I checked if the files could be downloaded and yes, they could be found under wp-content/upgrade.

I did have another problem, that might be related: I couldn’t upload pictures anymore as the folders that have been made by wordpress itself did not have enough rights. I had to delete them and build them new with more permissions. Now it works like a charm (till 2016, I suppose).

I am completely lost now. I don’t want to update manually. Any ideas?