I came across some worlds on PC which are failing the new server side checks and I don't believe they should be. These are worlds I've visited many times in the past without any issues.
wrld_18962fbd-f63f-4e5b-89ae-760f026f33d8 [Plum Pavillion Night - Silent]
wrld_1fee0d73-7e4a-4119-92bb-cf1c1c785971 [Skyline Café (v3.0) - Chengi]
wrld_a86dd689-dd46-4478-bd6d-63dd0d6818df [BI-Tan's Domain - WuWanan]
wrld_619f6bc0-f30b-4c03-b0a5-6cbb043a094c [English Cottage - Adi․]
wrld_4ff1d7e0-1290-421c-881c-e1a117b25aa4 [Snowdin HD 2.0 - Latiprod]
These show in the logs as "World 'wrld_...' did not pass initial checks and won't be downloaded: 10", then I'm sent to my home world immediately without any explanation in the client.