Transactions dis- and reappear from txpool_inspect at random

I'm implementing an application inspecting the ethereum mempool at regular intervals via the geth call txpool_inspect. There I have observed some strange behaviour, for some wallet addresses the transactions seem to go missing at random and then reappear on later queries.

I'm not sure how to create a long-term reproducible example for this, but, as of the time of writing this, the call

curl $MY_ETHEREUM_RPC_URL \                                                                    
  -X POST \
  -H "Content-Type: application/json" \
  --data '{"method":"txpool_inspect","params":[],"id":1,"jsonrpc":"2.0"}'

will produce a result containing the address + the transactions by nonce for the address 0x8a6bd90abb79ba36266c881561d5d0b1dc528f80 on some calls and on other calls not contain it. Even though the transactions in question have been in the mempool for 3+ days.

Can this behaviour be explained somehow? Is txpool_inspect not expected the return the entire contents of the mempool at all times?