I work on one community with phpbb3 forum, i do this job for 4-5 years and this is first time that i need support

First things about forum:
phpbb version: 3.0.14
Database server: MySQL(i) 5.6.34
3 edited styles in use (Fatality2016, red and orange)
Forum path: ...example.com/forum
We have 3 styles, 2 working good, but on third we have problem with acp link on the bottom of the page.
Red style and orange are edited version of Codfaction theme, and they are same, only colors are different.
PROBLEM:
When i click on "Administration control panel" at the bottom of page, it just redirect me to index page (like logged out but still logged in)
That index page where link redirects me is old one, new index page not looks like that for few months.
When i go to other themes and login to ACP, on orange theme ACP link redirects me normal to acp.
So problem is only when i am not already logged in to acp.
- When i click on ACP link, in browser i got this link: http://www.example.com/forum/adm/index. ... xxxxxxxxxx (my sid, and correct sid)
- Orange is not default theme.
- I have not installed new mods last few months
i Will post some images here about problem.
Image when i am normally logged in: http://prnt.sc/dpjjon
- look at things that are now on forum they are on that image
2 Images when i click on ACP link in footer:
First image (top of forum) http://prnt.sc/dpjk6s
Second image: (middle of forum) http://prnt.sc/dpjkld
On images you can see 5 numbers, here is explanation:
1. This shows that i am not logged in
2. this show that i am logged in (correct)
3. this elements we dont have anymore on forum
4. This board has no forums (but we have 26573 topics)
5. Here is top five mod, with best spammers, most thanked users...
If someone can help me please write here, thanks a lot.
p.s Sorry if my English is not perfect.