Thats actually been going on since 4.8 in PIE.
Has something to do with the mouse moving, and occasionally gpu particles also spawn at 0/0/0
Not sure why, but I have lived with it for a while now.
This might be related to a bug report I posted a while back (which has been fixed 
Thank you! )
But the symptoms are very similar.
The particle systems on my project seemed to be broken (ever since I switched to 4.11 from 4.10.4). I am on 4.12.3 now and I been living with that but I thought it was time to figure out what going on.
Just like the last time, I created a new project and added a simple widget with only a Text block in it. I added a GPU particle system and a CPU particle system to the level.
After about 5 seconds of going into FULL SCREEN, the particles freeze/get broken. This only happens in PIE (just like last time), it doesn’t happen in standalone. And if I minimize the window they start working again. If I go full screen again they freeze again.
If I remove the widget from screen (which consists of only a text block on the screen) the particles start working again normally.
I also tried the Content Examples, the 4.12 version of them. The Effects map and the Blueprint Communication map (the one where you shoot at the wood and ice spheres.) Many of those particle systems get broken if you go into full screen in PIE (when you add a simple widget consisting of a text block to the screen)
When you remove the widget they start working again normally.
Hey Shogo999,
Thank you for providing a detailed description of the bug, as well as the example video. It made reporting this bug much easier. I have gone ahead and entered a report for this issue, UE-32522. Once the issue has been addressed by our engineers, the fix will be added to the release notes for fixed issues within an upcoming full engine or hotfix release.
As a note, I did discover that toggling the console command will temporarily cause the particle system to update, as well as the workaround you mentioned by removing the Widget, or un-toggling fullscreen mode.
Let me know if you have further questions or need additional assistance.
Cheers,
Thank you! Glad I could make the reporting easier for you lol. I also noticed that when you compile shaders they start working again too. (say you have a landscape that takes a while to compile shaders, while the shaders are compiling the particle systems work again, when it done compiling shaders they freeze again lol)