You may be experiencing random browser issues. I'll help you check to see why you getting an error.
We can start by signing in to your QBO company using a private window. This step will disable the extensions and stops the cache from saving your search history.
Google Chrome: Ctrl + Shift + N.
Safari: Command + Shift + N.
MS Edge and Firefox: Ctrl + Shift + P.
If private browsing lets you enter time entries, you can clear your browser's cache. If it's the same thing, please use a different browser to see if this only happens to the one you are using.
Feel free to go back to this thread if you need more help.