Updating Craft (and sometimes plugins like Commerce) through Craft 3 admin gives errors. Usually undefined, but have gotten "Backend fetch failed" most recently. Once I refresh the window, it seems to be updated. Since the prior update pseudo-failure there was a message about maintenance mode and a button to continue (which I'm assuming is a flag set somewhere from the prior update). It's a live site on shared open_basedir hosting and proc_open() disabled—which is accounted for in the general config, disabling backups when updating.
Anybody experience this and/or have a solution? All the folder permissions and so forth look correct.