Hello,
I reinstalled the game (1 year of absence) and since then I haven’t stopped having drop frames all the time and with each game, every 3-5 seconds I drop from 120fps to 0. Before I had no problem.
That can be due to network communication issues between you and the Blizzard servers. HotS uses a lockstep game engine so if communication is not perfectly reliable (if dropped packets or delayed packets occur frequently) the game will have to pause to wait for server and then fast forward to catch up with the server creating a sort of stutter.
If using wireless this is likely due to packet loss caused by it, in which case the solution is usually to use an ethernet cable connected directly between your computer and your local network infrastructure. If you already are using a cable, then you may need to use tools like WinMTR, as recommended by Blizzard support, to try and track down where the packet loss is occuring.