The launcher works fine, but after clicking "play" Minecraft never completes loading. I've tried both launching version 1.14.4 or 19w42a and in both cases the status bar reachs quickly about 80-90% of progress and then stops. Thereafter nothing else happens.

However, sometimes it works. Say around 10-20% of the times. But it doesn't help to try like 10 times in a row, because if it starts with a fail, it will keep on  failing. But for instance I can play in the morning, then if I try in the afternoon it just won't start.