Actually, might be related.
Similar to Refrain from “Tor over Tor” Scenarios.
If a server is the first in the chain and the last in the chain (or potentially in the middle of the chain?) that might lower anonymity due to end-to-end correlation attacks.
We’re also avoiding to use the Tor network (as Tor) as well as the Tor infrastructure as a time osurce.
Similarly, using a VPN provider as both, a “first relay” (since using that VPN) as well as time source might be a bad idea.
So since we’re not short on time sources at this time, for abundance of caution, it’s best to avoid using VPN providers as time sources.