Could it be: No stamina recovery by watching ads?

Speaking from experience, when I try to recover stamina with ads, it often says there are no videos available. So, I frequently check if I can watch an ad to recover stamina once I've recovered about half of it. I also like merge games, and when I run out of stamina and think, 'Huh, is it already over?', I sometimes put in about three merge games of a similar type and play them. Before I know it, my stamina has recovered. I'm a free-to-play player, so I don't use diamonds for things like the 'bubbles?'

Sometimes, if you press the '+' next to your stamina, a 'Watch Ad' option appears, letting you get +15 stamina. Also, in the shop where you buy stamina with diamonds, the 'Watch Ad' option that occasionally appeared for the stamina box item in the middle used to let you get it for free⚡ Other than that, when you press the ad playback button that sometimes appears for item refreshes in the shop where you buy items with diamonds, or for charge time reductions in bubble/merge games, and it says 'Ad playback failed (even though you could watch it...)' you sometimes get stamina +10 as compensation, but this might just be an issue on my end...? 🥲︎ Sorry if my explanation was hard to understand (>_<)