I think that you are being limited somehow by that electrum API, it only let you 6 tries?
I think that it should give you a more detailed error of why it fail.
I don't use electrum at this time ~~
my BOT is writed by python and bitcoinlib
about 6~7 second POST RatTX to
https://mempool.space/api/txI think I gave away too often and didn’t calculate BTC/kvB properly.

====== w.utxos_update()
Found 2 unspent transaction outputs.
Filtered unspent UTXOs: 2
UTXO 7855cf143b41f86b04f385423a000f7cd6456f0d1ad4a76a8d3bd4850f8c8c9e:1 - Address: 166Bitrbfa16oR7DKKSzgdhU4MpVKE4cKb, Amount: 429618 satoshis, Spent: False
UTXO ca4aa3bd9e38eba447bff85a000e74fc27ca3ca78f1295a8481e50af65fcd511:3 - Address: 166Bitrbfa16oR7DKKSzgdhU4MpVKE4cKb, Amount: 90000 satoshis, Spent: False
2024-07-28 09:42:08 (UTC+8)
Send_BTC : 502098
Send_BTC_Fee: 17520
unspent_total_value = 519618
●Response from mempool.space : sendrawtransaction RPC error: {"code":-26,"message":"insufficient fee, rejecting replacement c938ceda6608cf912dba5dda7b2979ed11fa287c67670b359d365b436445116a; new feerate 0.00051681 BTC/kvB <= old feerate 0.00307514 BTC/kvB"}
2024-07-28 09:42:15 (UTC+8)
Send_BTC : 484778
Send_BTC_Fee: 34840
unspent_total_value = 519618
●Response from mempool.space : sendrawtransaction RPC error: {"code":-26,"message":"insufficient fee, rejecting replacement 8bd50cf10b880973a65a37b78e10f7c64413a6b995f1b639d184a2518449fbf2; new feerate 0.00103076 BTC/kvB <= old feerate 0.00307514 BTC/kvB"}
2024-07-28 09:42:18 (UTC+8)
Send_BTC : 467458
Send_BTC_Fee: 52160
unspent_total_value = 519618
●Response from mempool.space : sendrawtransaction RPC error: {"code":-26,"message":"insufficient fee, rejecting replacement 8adcb6a53e6524ca8c5c6b819e14d17ed7842a5a10ff597d763ff8c964039695; new feerate 0.00154319 BTC/kvB <= old feerate 0.00307514 BTC/kvB"}
2024-07-28 09:42:24 (UTC+8)
Send_BTC : 450138
Send_BTC_Fee: 69480
unspent_total_value = 519618
●Response from mempool.space : sendrawtransaction RPC error: {"code":-26,"message":"insufficient fee, rejecting replacement cc0d34c088e6e62a077ccd154db7cc0d4b0789d4a3a649c4907193d4d48412f3; new feerate 0.00205562 BTC/kvB <= old feerate 0.00669492 BTC/kvB"}
Send_BTC : 432818
Send_BTC_Fee: 86800
unspent_total_value = 519618
2024-07-28 09:42:31 (UTC+8)
●Response from mempool.space : sendrawtransaction RPC error: {"code":-25,"message":"bad-txns-inputs-missingorspent"}
2024-07-28 09:42:33 (UTC+8)
Error: Unable to send transaction (status code: 429)
●Response from mempool.space : <html>
<head><title>429 Too Many Requests</title></head>
<body>
<center><h1>429 Too Many Requests</h1></center>
<center><h2>Sign Up for <a href="https://mempool.space/enterprise">Mempool Enterprise</a> to get increased API limits</h2></center>
</body>
</html>
....
....
....
then~~~All response is "429 Too Many Requests"