Update

We've identified the issue and are working on a solution. Important things to keep in mind:

• Lost Gems will return to your account later today, we need to ensure they are properly calculated and no one loses anything
• Market Refresh will still subtract Gems from your balance past the full implication of 1.8, but those should be returned upon a game restart (no matter how many it took). That is the main issue we are working on.

We are also aware of lag issues that affect certain devices, the compensation for those will be handled separately.

Update #2!

• Our algorithm is hard at work now, returning the Gems that were lost. Per my information, it's almost done now, so your Gems are either already back on your account or should be before the evening is out. 
• Update 1.8.1 is out, it's aimed at fixing performance issues that affect a number of devices (Huawei and Meizu are among the most prominent ones). You can go to Google Play and update it manually now!