Safari bookmarks live there own lives in the same Apple ID

Hello everyone here!

Guys, at first I want to say sorry for my English but I'll try to describe my situation

My name is Grigoriy. I'm from Russia, Saint-Petersburg.

My problem last from early august 2017 and Russian apple support don't know what is wrong.

Since early august 2017 I can't use iOS safari bookmark synchronization. It's just don't work!

I use my Apple ID on my iPad Air and iPhone 5S but when I do a bookmark on one gadget it doesn't appear on another.

Or I can delete any bookmark or bookmarks on one gadget but they will stay on another.

Russian apple support connected to my gadgets to see what is happening on a display while I was doing what they told me by phone.

At least they asked engineers and they asked me to collect iPhone and iPad logs into zip and send them. So I did all they told me.

After that they told me

1 - to try another wifi

2 - to install the latest version of iOS 11

3 - to continue use this Apple ID with the problem

I was shocked by their answers!

About wifi - I have second (old) Apple ID and all works great with the same wifi. So I thing there is nothing wrong with my wifi

I use iOS 10.3.3 on my both devices and I can't say they are working perfectly as they were working on early iOS versions

I know how iOS 11 works on iPhone 5s and iPad Air - awfully! Very very slow!

So I don't want to kill my iPhone 5s and iPad Air with iOS 11.

Moreover nobody in Russian Apple support understand what's wrong and nobody give me any guarantees that iOS 11 will solve the problem with safari bookmark synchronization.

In best way I'll have very slow and stupid iPhone and iPad without problem of synchronization

In worst way I'll stay with very slow gadgets + the same problem.

It's my first appearance here so I'd like to hear any thoughts or deal advices from foreign Apple support to solve my problem.