Tatoeba is slow and I keep getting logged out. Sometimes it can take 30secs to 1 min to add a sentence. Sometimes the sentence is never added. Also, sometimes Tatoeba asks me to log in, but when I refresh, I'm logged in again. I often get "An Internal Error Has Occurred" when trying to load the homepage. I think Tatoeba is very close to not being usable right now.
Tatoeba has been slow for me for some time. Searches can be extremely slow. Entering sentences or translations regularly takes a long time, too. So does loading the home page. Pages of particular sentences do not seem to be affected by that issue so often.
Tatoeba has been slow these past few days mostly due to the search. The "internal error" you've got on the homepage is because the random sentence relies on the search. I assume the search was failing and as a result the homepage was failing as well.
When issues with the search happened last time, the problem was due to too many changes happening in a too short time. It created a sudden spike in workload for the search engine, it couldn't handle it. This time I'm not 100% sure, but it's likely for the same reason.
Note that "too many changes" doesn't necessarily mean too many sentences added or edited. It can be any change on data that the search needs to handle: tags, lists, owner of sentences... So it's not necessarily obvious what causes the search engine to breakdown.
The current "quick and dirty" solution is to disable the search from the website, run some script so that the search finishes its usual background tasks in peace, then re-enable the search once the background tasks are done.
This makes the website usable again for some time, but slowness will come back as soon as the search is being overwhelmed.
The longer term solution would be to optimize the search feature. That would include migrating to another version of the search engine. But it's a pretty big effort and we'll unfortunately need to wait at least another month before anything can be done about it.