The mempool of a node is limited in size (300MB by default). Once it's filled and the node keeps receiving transactions it will start evicting some transactions. The transactions less attractive to miners are (supposed to be) evicted to let room for higher-fee-paying transactions.
As pointed by @Murch in his own answer, there has been more than 300MB of backlog across the network at many points in the past 3 months. Most of it paying more than 1sat/vb. Your transaction must have been evicted from your node's mempool (and most likely from the mempool of its peers as well).
sendrawtransaction of a child (a transaction spending some of its outputs) will fail, since the inputs of the child would appear to be inexistent to the node. You should first rebroadcast the parent (the initial transaction), and then the child, for it to succeed.
Note you're only able to do this because your mempool isn't actively purging transactions at 1sat/vb at the moment. Otherwise you would have to submit both your transactions as a single package. This feature isn't available yet (as of October 2023).