I have a similar issue! I am comparing the test versions of Premiere Elements 19, Wondershare Filmora 9 and CyberLink Power Director 17 on my Windows 10 PC.
Premiere Elements is my favorite, but when exporting my test video (30 seconds long) in 4K (MP4), the result is very disappointing! Some sequences are OK, but zoom-ins are stuttering and at a certain point the video freezes with colorful artefacts (like a tv tuner losing the signal). I repeated the export, but result was the same.
I would not expect 4K-teething problems in Premiere Elements, but what else can be the reason?