Cannot get to admin panel after upgrade

Hello,
I am new to Grav.
Well I tested it a year ago and today I came back to that old install (on OVH). I went to the admin panel ans did upgrade Grav, then upgraded all the plugins. And all went well it seems.
But then, after closing my browser tab, it was impossible to get to the admin panel again, no login form, nothing.
What should I do ?
Thank you for your help.
(I could reinstall since the site is empty, but I would like to understand what went wrong, in case it happens when I am working on a real site.)

Hello @Keith

I had the same problem, this may not be the best solution; but by restarting apache I was able to login as if nothing has happened.

Hello @ryan
Thank you for this idea. Unfortunately I don't have the power to restart Apache on this shared OVH server 🙂

can you try this?

bin/grav clean

bin/gpm self-upgrade

bin/gpm update

Thanks for this idea, I did that :

$ bin/grav clean
DELETING
file: ~/www/grav/user/plugins/email/vendor/swiftmailer/swiftmailer/.travis.yml
file: ~/www/grav/user/plugins/email/vendor/swiftmailer/swiftmailer/composer.json
file: ~/www/grav/user/plugins/email/vendor/swiftmailer/swiftmailer/.gitattributes
file: ~/www/grav/user/plugins/email/vendor/swiftmailer/swiftmailer/.gitignore
dir:  ~/www/grav/user/plugins/email/vendor/swiftmailer/swiftmailer/tests
dir:  ~/www/grav/user/plugins/email/vendor/swiftmailer/swiftmailer/doc
$ bin/gpm self-upgrade
GPM Releases Configuration: Stable
You are already running the latest version of Grav (v1.5.8) released on Fri Feb  8 00:05:27 2019
$ bin/gpm update
GPM Releases Configuration: Stable
Nothing to update.

Now I still have my 404 error when going to my admin personalized URL just like before, but also I get this bug when I get to the grav folder URL (I think I did not have that before but not sure about it) :

Server Error

Sorry, something went terribly wrong!

0 - An exception has been thrown during the rendering of a template ("array_chunk() expects parameter 1 to be array, null given").

For further details please review your logs/ folder, or enable displaying of errors in your system configuration.

yuck... maybe its just best to backup your user dir and re-install?