Yeah, my guess is the outbound connection at home. The T-Mobile 5g router is undoubtedly optimized for inbound not outbound and in the evenings it gets congested (my suspicion)
I could try running Tailscale on the synology rather than from within Channels.
I notice than when buffering happens, i stop and back up the show just a bit and it gets past the stop point. That leads me to think if i could increase a buffer size, it might be able to mitigate at least some of the issue.