In my different campaigns (content sharing enabled in both) Patrons options for Warlocks somehow looks like 6 Patrons on one and only The Fiend in second one. Any suggestions how to resolve this issue? 

Hello Toledo!

It sounds like in the first campaign one of the players owns content from the Player's Handbook and Xanathar's Guide to Everything, which is being shared to you. In the second campaign if no player owns that material, it can't be shared. 

If someone in the second campaign can verify that they own that material on their account, try turning content sharing off and then back on.

Let me know if this helps.

Thank you. You were absolutely right.

Also, to note, content sharing is only availlable int he said campaign when it comes to character creation. meaning you absolutely need to create a character in that campaign.

so if like me you have players wanting to create characters on their builder but did not buy any books, then they require to do it in the campaign itself. not on their account.