No problem with your language, I'm not native English either.
Well, yes it may be due to RG limit. From what you describe, the rest of parameters to check are completely out of reach anyway. Like connection PAR quality etc...

 

Last edited: Mar 11, 2022

Can I ask you what is connection PAR quality, I couldn't find anything online in regard to that acronym (PAR)

 

I don't know the exact name in English. Maybe it's called a pair.
I was speaking about the physical connections out of your house, where different lines are grouped, and then go to a connection center. If this particular connections are bad, you can experience instability even with optical fiber.
It once happened time, and it was hard to convince the company that I knew better than them what was happening, but at the end they changed the "pair" to which my line was connected and everything went as it should after that.

 

Ok, I understand what you're saying. I don't think that is the problem cause in command line speedtests I have 2.4Gb/s band with minimal jitter and 0% packet loss. Although speedtests don't match real life connection speed they can be used to have a proof that the connection itself is working as it should. Thanks for all of your replies, much appreciated.

 

So, you've reached the speed limit for RG.