I'm now wondering if a reinstall may fix the issue you have with the pre-set templates. Are you able to replicate the issue using the 'color patterns' or sample videos? If you can, then definitely think about replicating it with Live Screen Capture tool and speaking with Corel. It might be that they will suggest a reinstall or something else.
Whilst I did use IP-01 for a recent project, I think that I'd prefer to create my own in the future. I'll see though. I often like to use the template for inspiration once I've got the hang of things or I'll go back to them for speed when it's more useful to get a new project out sooner. What I'm suggesting is that there is no harm in not using the templates, but perhaps you could use/pinch their ideas and make something of your own from them.
The little 'FX' is perfectly normal for the Split Screen. If you look you'll see that for the placeholders the 'Geometry Mask' effect has been added and for the 'SplitLines.png' file the 'Split Graph' effect has been added. This is how Corel are managing the split screen effect.
Currently, you can't edit these effects. I would love the ability to do so and change a few items, such as the line colours, width and perhaps when some of them come in or leave.
So for now, the little FX is perfectly alright.
As for replacing the placeholders with your own content, as with anything to do with computers, there is more than one method. The way which I described above works. I wanted to see if I could find a video showing it to try to make life easier for you. Whilst looking I found an old video from Gripps. It shows another method (quietly swearing under my breath here), which also works with the split screen (I checked).
https://youtu.be/bUdIlUMSFSk
I have found an old video from Corel too. It does use the method I've described above.
https://youtu.be/sgMIhtUxusI
Hopefully, they will be of use to you.
I was going to look at that website mentioned in the video which I didn't know about previously (
http://photovideolife.com ) but sadly it appears to be closed now and redirects to the Corel.com site instead.