Difference in timeline play and slide preview, and video freezing

Hello, I have an annoying problem. When I test how I allying videos with narration and objects I would like to use timeline.
Please look the explanation in the attached video. That's bothers really.

First I tried to make it with 2-min video and put cue points and start and pause the video when my narration needs more time. It doesn't work as well (see the attached .story file).
Then I spent time and cut my 2-min video into pieces, but anyway I have my videos freezing now.
I'm using Win 10. 64-bit. And my storyline version is v3.43.22859.0.
I made the diagnostics. Says all fine.

User Authentication: Success
Authentication (https://id.articulate.com/): Success; Online; 1.4s
Desktop Apps and Updates: Success
Desktop Apps and Updates (https://api.articulate.com/products): Success; Online; 819ms
Desktop Apps and Updates (https://api.articulate.com/products/stable): Success; Online; 814ms
360 Synchronization (): Success; Online; 3.6s
Content Library 360 Characters: Success
Characters (https://api.articulate.com/content-pass/characters): Success; Online; 1.4s
Content Library 360 Images: Success
Content Library 360 Images (https://api.articulate.com/content-library/images?query=diagnostics&type=photo&page=1): Success; Online; 980ms
Content Library 360 Templates: Success
Templates (https://api.articulate.com/content-pass/templates): Success; Online; 2s
Team Slides: Success
Team Folders (https://api.articulate.com/team-slides/folders): Success; Online; 344ms
Team Projects (https://api.articulate.com/team-slides/templates): Success; Online; 667ms
Publish to Review 360: Success
Review 360 Items (https://api.articulate.com/review/items): Success; Online; 164ms
Notifications: Success
Notifications (https://api.articulate.com/products/notifications): Success; Online; 185ms
Remote Features: Success
Remote Features (https://api.articulate.com/products/features): Success; Online; 192ms