When you clicked send, did you get any sort of error message at all? If the transaction was not broadcast correctly, it should really having given you some sort of error message to explain why it was rejected.
A "too low fee" at the moment would not prevent the transaction from being broadcast... the mempool min fee rate is 1 sat/vbyte... which is also the minimum possible transaction fee rate. So, at worst, your transaction would just be "stuck"... but would still be in the mempool.
So, either your wallet file itself is not "synced" (even though your
node might be fully synced with all blocks downloaded)... and it needs to be rescanned.
Try using the
rescanblockchain command on the console... note that this could take an hour or 2 to complete and will likely render Bitcoin Core "unusable" while it is rescanning the wallet file.
And you may need to rescan each wallet file individually.