I had the same problem when upgrading one of my Grav installations last night (I also updated plugins at the same time). The install now seems to have worked but I get the following error whenever I load the main admin page:
Fetch Failed:
Cannot read property 'forEach' of undefined
TypeError: Cannot read property 'forEach' of undefined at t.value (http://[path to Grav]/user/plugins/admin/themes/grav/js/admin.min.js?d5f052cd07:4:2368 2) at http://[path to Grav]/user/plugins/admin/themes/grav/js/admin.min.js?d5f052cd07:4:2286 2 at http://[path to Grav]/user/plugins/admin/themes/grav/js/admin.min.js?d5f052cd07:4:2190 9
Invalid SSL certificate caused by CURL error number 60
This error pops in a red box in the admin then fades out. Everything appears to work ok. I've tried clearing cache in the admin but to no avail. My other Grav installs updated earlier today with no problem. Is there a fix?
(I don't know if the SSL error is related.)