How to find a file which can't be found on macOS Big Sur
I see the exact same thing. I noted the time (09:35:25) and found this in Console:
Nov 14 09:35:24 Honu amsaccountsd[673]: objc[673]: Class AMSDaemonConnectionInterface is implemented in both /System/Library/PrivateFrameworks/AppleMediaServices.framework/Versions/A/AppleMediaServices and /System/Library/PrivateFrameworks/AppleMediaServices.framework/Versions/A/Resources/amsaccountsd. One of the two will be used. Which one is undefined.
Nov 14 09:35:24 Honu amsaccountsd[673]: objc[673]: Class AMSXDProtoMessage is implemented in both /System/Library/PrivateFrameworks/AppleMediaServices.framework/Versions/A/AppleMediaServices and /System/Library/PrivateFrameworks/AppleMediaServices.framework/Versions/A/Resources/amsaccountsd. One of the two will be used. Which one is undefined.

Nov 14 09:35:25 Honu MRT[674]: getattrlist failed for : #2: No such file or directory
Nov 14 09:35:29 --- last message repeated 2 times ---

Nov 14 09:35:29 Honu mdsync[694]: objc[694]: Class MDSPathFilter is implemented in both /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/Metadata.framework/Versions/A/Metadata and /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/Metadata.framework/Versions/A/Support/mdsync. One of the two will be used. Which one is undefined.
Nov 14 09:35:30 Honu com.apple.xpc.launchd[1]

So it seems to have to do with something called &quot;getattrlist&quot;.
Here's a link that might be of help:
https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man2/getattrlist.2.html
That said, I still don't really know what this is but now I now know that I'm not the only one with this issue.
I know that this is likely not much help. If I find out more, I will post back.