After one sec realized it could be not Ad block.
1) I had Adblock running on Chrome Polish language. I see no "Enter Combat" sign next to "Ready" (I saw it on FF, also I saw it on Dev version - logged once, week after you relese combat, I think)
2) turned Off adblock, refresh browser (by refresh button), and "enter Conbat appeared.
3) After Turning ad-block on I can enter combat. Strange. Either ad-block or refresh helped.
I know, I should post separate bug-report. sorry.