I mean wrong calculation of fees like over paying or paying less than what mempool suggests us to use.
it's mostly based from Bitcoin Core's estimatesmartfee which gets its estimation on the previous blocks and mempool.
It usually overpays/underpay if the previous blocks have more high/low fee rate transactions than usual.
Anyways, I'm telling OP that his fee rate is "alright" and setting an example that will likely not require him to increase the fee rate than what he usually pays,
he don't have to increase it in all situations:
As long as it's telling you "In the next block" or "Within the next 2 blocks", the fee is alright.
The issue was: there's an unconfirmed parent transaction.