tl,dr: computer hung on a boot screen, problem went away, then "experienced and internal error" the next day.
I have had Ubuntu installed on my secondary computer for a little over a year. I have not installed any new hardware into the computer. The computer has never had a problem booting before this. But, it hung on the screen that says Ubuntu with the 5 dots that light up sequentially. The computer stayed on that screen for about 15 minutes with the 5 dots lighting up sequentially (normally it would stay on that screen for 45 seconds or less). I wasn't sure what to do so I pressed a couple of keys, one of which was ESC. Next, the dots stopped sequentially lighting up, and so it seemed like it was frozen. I gave that 15 more minutes with no change to the display. So, I held down the power button (it's a laptop) to power it off.
Next, I booted while holding down the shift key. The idea behind that was to see if the bootloader screen would come up. When that came up, it showed 3 different versions of Ubuntu. All were 18.04, with the numbers after that being different. I didn't think it would look like that but maybe that's normal. For each of the versions, there was also an option for safe mode (or whatever Linux calls it). I chose the most recent version and safe mode. The computer then ran through a bunch of text information and then wanted to know if I want to continue the boot process. I said yes and it booted into the normal looking Ubuntu with the Gnome desktop. Everything looked normal. I then booted the computer a few more times and everything seemed normal.
Here are the things that I did before the problem surfaced: I installed "Tweaks" (or some name similar to that) through the software manager. For this I had to install the dependencies, "notify-osd" and "overlay-scrollbar." I did that using the command line & apt repo.
Also, a couple of days prior, I installed LBRY. But, when I started that up, I got a message that that wasn't the latest version and so there might be security issues. So, I exited and never went any further.
The day after the boot problem, I got an error message, "Ubuntu 18.04 experienced an internal error." When I tried to view the details, it references the executable path,
The GUI also seemed like it was trying to load more details but it never came up with anything, after giving it a couple of minutes.
What can I do to address the issues/ unexpected behavior?