cs_desc_main is typically locked within scope of a cs_wallet lock, but:

CWallet::IsLocked locks cs_wallet
...called from DescriptorScriptPubKeyMan::GetKeys
...called from DescriptorScriptPubKeyMan::GetSigningProvider which locks cs_desc_main first, but has no access to cs_wallet
...called from DescriptorScriptPubKeyMan::SignMessage
...called from CWallet::SignMessage which can access and lock cs_wallet

Resolve the out of order locks by grabbing cs_wallet in CWallet::SignMessage first