Site integration was broken after upgrade

[atento]

Hello, I using a vBulletin's login engine to enable user access to hidden sections on other site.
This integration uses plugin-system with simplest setting-up a $_SESSION variable.

I have upgraded a forum engine from version 3.6.5 to version 3.6.6 with complete following instruction steps. But now I have debugged that $_SESSION variable was successfully set after plugin work, but with next page refresh variable is already empty.

It seems that session is not starting, or something like that, I haven't any ideas where is start searching from.

Thanks for your help.

[Boxy]

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