Again getblockchaininfo returns me the same height as mempool.space, and estimatesmartfee returns "Insufficient data or no feerate found". I am using CLN to open a channel
Hmm, estimatesmartfee just started working without me changing anything...
Changed the settings back to the original ones I had, restarted bitcoind, and fee estimation still works. Not sure what happened?
I believe this answer on Bitcoin StackExchange mostly answer your question.
The fee estimator tries to estimate the fee the balances between cost and time to be included in a block. It does this by looking at the fee rates of transactions that it receives in its mempool and seeing how long it takes for transactions at a given fee rate to be included into a block. It becomes more accurate as it sees more transactions and more blocks because it has had more data to analyze.
Just wait. Leave the nodes online. The estimators require data and the only way to do that is to wait. They become more accurate over time.
Ok, it is strange that there was no fee estimation after bitcoind had been running for months, then no fee estimate for 24 hours after restarting, then now it works regardless of if I restart it or not. Was it due to a lack of txs in the testnet mempool?