iMac 2017: User login only loads half way and then stops... but only once, when I turn the computer on for the first time in the morning.

Hey guys,

I've got a bit of a strange issue.

I recently upgraded my iMac's hard drive to an SSD. Everything works fine, except for when I turn the machine on for the first time in the morning. Without fail, the computer boots, I log in, user data loads... and then stops halfway. I then have to force a shutdown to get it out of the freeze. This has happened every day for the last week.

... And then I try again, the computer boots, loads in seconds, and everything works perfectly. Obviously, this is not a computer-breaking issue but it is rather annoying.

This is where it gets stuck and I have to force a shutdown:

Have you guys got any ideas on how to fix this?

Thanks a lot.