I recently installed an external SSD to move the system and apps on a 2013 Imac with latest version of Mojave. Since then I had it happen twice that the computer froze, both times I happened to be in Chrome. Then after about 10 seconds I got a blank screen and the Apple logo with progress bar came. After some time I got the Disk Utility screen and went tot he Apple logo in the corner and selected restart, After that it restarted normal and everything works fine. Wondering here where the problem lies. It could have been accidentally to happen twice in Chrome. But this only happened after putting the system on external SSD. Other than that no issues. Any ideas as where the problem could be?