We are currently working hard to introduce Rewarded Ads into Triple Match to extend the level and help our players on the more difficult levels.
Our developers are currently testing the rewarded videos feature. Therefore, sometimes, you might not receive the option to watch rewarded videos.
The availability of reward videos depends mainly on your network (Wifi/LTE/3G), a 3rd party ad blocker installed, etc.
Another reason might be "inventory" - advertisers place their ads in different areas and times.
Depending on your location and targeting (something Google does, as we use 3rd party partners - such as Google - to place ads), you might not receive ads sometimes.
Hence, we strongly advise the following actions:
1. Verify that your operating system is up to date (the game also).
2. Toggle between different networks and check if the issue persists.
3. Verify you do not have a 3rd party ad-blocker installed on your device.