No access for level 421 for days!

I finished level 420 and for days now the game won't let me access to next level which 421. I can see it and see that some of my friends are further advanced in the game but the game wouldn't let me access to it. I can play any other past level. It's not the first time that this happens. I guess I had the same issue at level 406. I have suddenly a message saying "further levels are not available at the moment, switch to candy crush saga for more fun"!!!

why is this happening between stages? It's becoming annoying! Please fix it once and for all!

thanks