I've included some pictures he sent to me showing what he was seeing. The first issue appears to be some sort of visual bug that affects changing terrain features, examples include The Community Center, the Abandoned Joja Mart, Pam's House, the Expanded section of Grandpa's Farm amongst others.
We have been experiencing the first issue since we started SVE at the beginning of April, whereas the second issue has only occured since the most recent update (1.13.3 at the time of playing). This is not a local network co-op its through the internet. We have had two issues so far, however both of them have only affected my friend not myself as the host.
I am writing today in the hope of getting some concrete answers to some issues that have been affecting a friend of mine while we've been playing SVE together recently.