Ingame cutscenes take long to load

I have weird problem with in game cutscenes. About 80% of the time, the window with character speaking appears on the left of the screen(the character face is not yet shown), then whole game hangs up to 10s, then it continues(and repeats with nearly every cutscene). So like if it was stuck in some loading phase or what. In WOL, all is OK, it is happening only in HOTS. No disk activity during this. Everything else runs normally, gameplay is smooth and on recommended settings. Windows 10, latest updates. Any hints on the cause?