Adobe premier pro Crash & Freeze

Hello to the entire Adobe community! 

My Mac : 

Mac Book Pro 2017

Processor: 3.1 GHz Intel core i5 Dual core

Memory: 8 GB 

Graphics: Intel Iris Plus Graphics 650 

I solicit you because I'm facing several problems: 

- 1 : When I export a video (1Go, sometimes less) of my software, Premiere Pro crashes completely. Of course, some After effect or motion design files are integrated, but nothing very big. 

Sometimes it shows me an error message, sometimes not. (picture 1) Sometimes my entire computer turn off because of it. (picture 2) But it's impossible to export my video. I have to split the export in several parts and gather the exports on a single final export. 

- 2: Previewing my video when I edit has become almost impossible, even in 1/4. I tried to empty the media cache, close all my other applications to free working memory, etc... But nothing changes. Impossible to work with the image that jerks like that. 

My software has been working very well so far. For the past month, I feel that it's losing some of its liveliness.

If any of you have a miracle solution to my problems I would be eternally grateful! 

I look forward to hearing from you, 

Have a nice late night.