Bad laptop performance: Lenovo Y50-70 (tested with multiple OS)

Question

Its my last attempt to get some insights with whats going on with my laptop. I had posted in the past a question about bad perfromance of my laptop (Unreasonable laptop performance) where I was explaining the behaviour of my laptop using Windows 10 and with a the default hybrid hard disk.

Briefly, my laptop generally had a delay in typing, delay in changing browser tabs etc. (and some other effects explained in the link provided before). And this was always happening around one week from a fresh format. One week of everything performing normally and after slowly this delay was starting and going even worst etc.

I had some recommendations of checking for updates for windows 10 and some recommendation of changing the hybrid hard disk with an SSD.

And here I am now: I have upgraded to an SSD and changed Windows 10 with Ubuntu. One week of great performance and after again some of the problems: Slow typing in browser, slow typing in installed softwares, delay to enter any website, delay to close a tab(both in browser and in installed softwares).

And my questions are:

What else can it be?? ..

Does this behaviour clearly indicates that there is a hardware problem? ( as most of the same problems occurred also with ubuntu).

How can 1 week of good performance and after that bad performance can be explained?

Is there a way to measure this performance (specifically the key delay performance and the delay to load a website) in order to evalaute that there is a problem and not everything is in my mind?

And if there is not a solution how can this problem be reproduced by LENOVO technical support in order to get a replacement? (I mean if i send it to Lenovo they will probably just make a format and see that the laptop is ok, and they will just give it back to me.)

Any insight for any question would be grateful. Thank you.

Note: I am a responsible user and give attention to the maintenance of the PC

Edit:

Running sudo memtester 1024 5 in one of the tests i got the following error:

Bit Flip: testing 153FAILURE: 0x00080000 != 0x00000000 at offset 0x1cd43230.

Run again the test and had a failure in:

Checkerboard: testing 44FAILURE: 0xaaaaaaaaaaa2aaaa != 0xaaaaaaaaaaaaaaaa at offset 0x05edca38.

Could it be RAM problem then?

Edit 2:

I have also noticed that this behaviour is kinda random. There are times that I open my laptop and the behaviour is pretty close to desirable and there are times that that I open it and its super delaying in typing.

Edit 3:

Tried memtest86 for whole night gave zero errors. How much sence it makes that onse i had error from memtester and using memtest86 didnt? I have read somewhere that I one time there was error output then the RAM has problems whatever happens with next tests. Any thoughts?