How to bypass square brackets in cookie name in GTM?

Question

Google Analytics

Hello.
Enabled user-id for the site in analytics. In the tag manager, in the analyst counter tag, I added &uid, and in the variables I created a 1st party cookie and specified the name of the cookies. Everything as described by Google: https://support.google.com/tagmanager/answer/4565987
Name: InstantCMS[userid]
As you can see from the name, it contains square brackets. In debug mode it says undefined.
The problem is exactly in square brackets, because I changed the cookie name to another one where there were no brackets - everything worked.
Can you tell me how to bypass this?
Thank you.