Good morning, 

Purchased and downloaded FTB Oceanblock from Minecraft Marketplace.  Game opened and I was able to do the intro (find the buttons) but when choosing an island, the game remained at "Loading Island" for all five islands.  Tried leaving system open for 30 minutes but it was still "Loading Island".  Music was playing, could look around and move around a bit.  Could even see the island and surround terrain, but the game would not continue.  Submitted the issue to Minecraft Marketplace who quickly replied that this is a known issue that is being worked on, but also recommended submitting the details here for moderators and developers to collect more information.  

Hope this is resolved soon because it is always a disappointment to purchase something and find it doesn't work (definitely not what I would expect from the FTB team).

All the best, Liann