Every single player is able to reach 5 stars in every hotel and, thus, they will be able to unlock further levels. Objects paid with gems won’t affect this progress.   

Double-check the small yellow wheels that appear in every room and services' object windows. They must be 100%. You can swipe sideways easily from room 101 until the last one checking these indicators. ALL of them must be at 100%, as well as all the staff available hired.
 
If you don’t achieve the five-star rating at your hotel, double-check ALL your services and rooms objects, such as parking features (security cameras in Blue Crystal Resort), restaurant decorations (especially at Stanley Resort, because you need to scroll down), hire all the employees available, etc. Once you fully upgrade the hotel, you will get five stars.

 

You can easily check which room or hotel service needs to be maxed out by tapping on the stats button (right side icons of the playing screen). You will find a progress bar for all your rooms and also a tab with all your hotel services and their progress percentage. You just need to tap the “Go To” button to find the pending upgrades.
 
If everything is maxed out, please try to fire and hire employees to stimulate server calls from your game (if this doesn’t work, you certainly need to look for upgrades).