Modpacks crash right after startup

[4net_E]

LAUNCHER VERSION: v4.664

OPERATING SYSTEM: macOS 10.14.6

JAVA VERSION: Oracle 1.8.0_261 64-Bit

ANTIVIRUS: none

recently I tried to play some modpacks, but i couldnt start any of them. Every time I wanted to launch them, icon of the modpack showed up in taskbar, window popped up, but after approximately a second, it had crashed.

I tried to solve this problem by myself, but I didnt manage to success. The closest Ive got to solution was in this thread :

However, there is a solution linked on another forum thread, but that link is probably corrupted or something, as it just redirected me to the same thread all over again. Thus Im stuck and seek help. This is a log after one of the unsuccessful launch attempts: https://pastebin.com/Md4yW3yw

For any kind of suggestions or additional information request I'd be very thankful

Okay, fortunately under this post's recommended threads I've found another new thread which stated a similar problem: 

 

The solution right there seems to do the job (at least temporarily), but still, I'd like to know the core of the problem, for example - why 8u251 works and 8u51 doesn't?

Hope this helps someone someday