Unhappy [Q] strange lag+keyboard

Hello guys!

I have a samgung galaxy note 10.1 (2014 edition).

I have noticed that when I type a lot characters (above 5 lines) in a field starts lag . The strange is that lag exists only in this field and all others go smooth.

For example if in 920 text editor I write 10-12 lines there will be lag in writting, but if I open a new tab (without closing the other tab) I can write smooth.

I tried to open large text files and I can write smooth but then when i type some lines lag starts again.

I have tried a lot keyboards but I don't have found solution.

So, is this a ram problem? How could i fix this? I can't think a reasonable reason.

Thanks a lot and sorry for my english.