This sounds like a particle bounds issue. Open your particle system in cascade and click the bounds button located at the top then select “set fixed bounds”. Make sure the fixed bounds are large enough to accommodate your issue.
If the problem still persists I will need a screenshot of your particle system open in cascade with the required module selected.
If your particles are moving it is possible they are moving outside the bounds. Make sure the size of the particle bounds is large enough to contain the area they will move into. You can find this setting by clicking in the blank area in cascade next to the emitter. I highlighted the values you need to change.
The post you are replying to is really old. They might have changed where they put options like this.
If you are having a bounds issue, I believe the Cascade toolbar still has the button at the top to quick-fix it.
Also, if you are looking for it in the details panel, you could try clicking in the blank space with no emitters (to get the general details) and then type “bounds” in the details search to see if there are any options there.