Hello.
It is a correct survey exported from limesurvey 5.3.

Tryed to import to 5.6 and 6.5 limesurvey scripts with no errors, but still exists "cannot activate survey 'too many questions'"

I think it is innoDB MySQL engine 1017 columns number limitation in table.

Is it solvable?

Three questions and more than 1000 columns?
Really?
But it is not solvable. InnoDB allows only 1000.
MyISAM  allows more. Ready the Manual For Details.
You should really revise your survey design.

Sure MyISAM did, but it locks project token table for any read until all new tokens uploaded.
So uploading a lot of tokens, 1000000 or 2000000 and more, stops all intervievers for about half an hour. They can`t start new survey until token upload finishes.

Hi,
I see, you know.
So you have to decide.
Revise the layout, change the engine, or ...
Write a letter to Monty Widenius, that he raises these limitations of MariaDB. 

 

I still dream about about "settings -> split survey table" option. May I?

You may. But this dream has been dreamt for many years now. So I wouldn't get my hopes up too high. I am sure there is a feature request somewhere. You should add your thoughts to that.