Footage Glitching Heavily + Jumping Frames

Hi!

I created a new project in Premiere Pro 2019 CC (Windows 10 x64).

I imported my footage into the media browser.

As soon as I start previewing the footage, the image starts glitching a little bit.

It mostly jiggles and randomly starts over/shows random frames in the middle of the video while playing back/previewing.

As soon as I add the footage to my sequence, the glitching, jiggling and frame jumping gets worse and I cannot normally use my videos.

I recorded it so you can have a look if you'd like to (skip to 0:20): https://youtu.be/lzH1M14FHiU?t=20

Adobe Premiere Pro CC 2019 - Glitching Footage - YouTube

Edit: Explanation of the video:

I just noticed that the cursor also jiggles on the timeline when the glitch happens (see 0:35).

Also, the video starts over from frame 1 at 0:36 although it still has about 20sec of footage to go (behind the "In" marker I set in the preview window).

This persists even after exporting the movie.

Here are the project specifics:

Sequence: 50fps, 1920 x 1080 (matching footage)

Footage: Mostly 120fps and little 30fps (.MOV, recorded with iPhone 7) - interpreted as 50fps assumed frame rate (the issue also occurs with other sequence settings and with original frame rates)

Imported Media: around 1,400 .MOV file (avg file size might be around 25MB)

When I open the videos in Windows, they play back normally. The files are not corrupt.

I tried importing the footage from both a HDD and a SSD - this makes no difference.

My Laptop:

HP ProBook 470 G5 3KZ06EA

Processor: Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz 1.99GHz

Installed Memory (RAM): 16.0 GB (15.9 GB usable) - I gave Premiere Pro the max RAM usage possible in the settings

x64-based Processor

Graphics: NVIDIA GeForce 930MX (DDR3) - 2048 MB dedicated memory

I am very thankful for any help, as my entire project depends on the solution to this issue.

Thank you!

Tom