Menubutton not appearing (mobile plugin)

Hi!
I'm working on a relaunch of a client site and I don't know what happened. I had fixed all css and adjustments in the new template (made with TC) and everything was working fine. Then I made some updates (J 3.9.0 to 3.9.1, AdminTools, Akeeba Backup, and latest maximenu CK) - now the menubutton is invisible. Using the default themes I can see the menu. As soon as I use the custom tab it disappears.

I thought it might be an outdated version of the mobile plugin and bought the latest. Unfortunately the problem remains. I need a reply urgent, as the site should be live tomorrow.

Regrads
Michael

Hi
Please give me the url of your page so that I can see the problem. If I understand the problem is related to the mobile menu ? are you using the plugin maximenu mobile, or Mobile Menu CK ?
CEd

MaxiMenu CK 8.2.18
System - Maximenu CK Mobile 2.0.24 (bought today)

Please delete the URL after you've read

go in the maximenu mobile plugin >> edit it >> save it (without changes)
tell me if it fixes your issue

simply opening and saving it doesn't make a difference.
I thereafter changed to default layout and saved - have a look I don't touch it so long.

The detection is by resolution ≤ 950px

I get this message now
"THIS SITE IS UNDER CONSTRUCTION."