I was on Explorer of the Seas last month. I only had the Voom plan for one day, but I did use the APP on my phone every day.
There were certain places/times aboard the ship where the WiFi connection was bad. To me, that meant that there wasn't a WiFi Access Point(AP) close to me, or it was over saturated with users. If that happened, I'd just try moving to a different location, and the connection would get better.
The older ships weren't designed with WiFi in mind, so adding the APs later on must have been quite the job. WiFi doesn't go through steel very well,. That makes it even more challenging.
Aloha,
John