I have been having the exact same problem. Also in Rinkeby. For me this started at some time between Nov 2, 2022 at 1:00 AM and Nov 2, 2022 at 2:00 AM Pacific time.
I created a new contract and minted some NFTs on this contract 0x98c72dcd0ef2da22311431c5572e6c49dac00da7 at 1:08 AM and it seemed to work fine. Metadata was loaded correctly and NFTs were available in the nft APIs.
When I tried to do the exact same thing on this contract 0x3e751082667b092fd542e3879f3037f10fa48e78 at 1:42 AM the metadata never loaded in Moralis APIs.
From @cryptokid post indicating the need to call syncNFTContract I checked out my contracts again. After invoking syncNFTContract my metadata for those contracts was populated correctly in the nft APIs.
Prior to September 2 I didn’t have to run the syncNFTContract against my collections to see metadata populate in the Moralis APIs, but it appears that now I have to manually invoke this command.
Hope that this is helpful to you!