I have more than one hundred workflows running selfhosted for many months.
In many cases, the Executions screen is empty or displays only the last few days, even though I have proof that it has been running on schedule for weeks.
That is possibly a good thing, If you have hundreds of workflows running and you are saving all executions on SQLite you will eventually have a bad time.
We have a default option that removes data after 14 days or 10000 records, It could be worth checking your env options to see if you tweaked any of the settings. I would look for EXECUTIONS_DATA_MAX_AGE as a starting point but you can find others here: Environment variables reference | n8n Docs