Looking at
https://bitcoin.stackexchange.com/a/92847, it seems Electrum create non-standard transaction. While it should be valid transaction if it's included on block directly, most node and miner/mining pool would reject it by default. So i would suggest you to follow @LoyceV suggestion to use newer version of Electrum securely, in order to re-create that transaction.
Hmm, yes, probably it is something like that. But there is no mention of "electrum" in your link...
I see you've found the actual problem, which is different case from link i mentioned above. But to be clear, i mentioned that link since it have same error when broadcasting the TX.