RB2011UiAS-2HnD

Upgraded to 3.36, I have no wlan interface and no associated menus.

Also, Downgrade didn't work.

Did you mean 6.36? What packages are installed and active?
Do you use winbox 3.4? Have you updated firmware after ros update?

Firstly, many thanks for your reply and my apologies for the brevity of my initial post.

Sorry, you're right - 6.36!!

I've been using Webfig but I can look in Winbox. No wlan interfaces are listed in /interfaces print, however.

RouterBoard is at v3.33 (latest at time of creation of this thread)

You hit the nail on the head with packages, the router had wireless-fp installed but it's vanished. I guess this happened when I copied the config from a hAP Lite.

I enabled the package, rebooted and the wlan1 interface reappeared but disabled. I've enabled it, but it's not running. Did this through the terminal, I'll have to set up a port forwarding rule on my AWS CHR to get into Webfig from my current location. Doable, but not in the immediate term.

To clarify, I guess the usage of wireless-fp happened when I copied the config. The disappearance is definitely the 6.36 wireless package change.

wireless-fp is no longer supported.  install wireless-rep or wireless-cm2.

Unfortunately it appears not to be as straightforward as just enabling wireless-cm2.

You should have done that before upgrading!
Next time it may be better to read the release notes before upgrading...
However, it would have been better when MikroTik has done more to draw attention to this.

Now, it is probably best to export the config and start with a new netinstall.

Having a working downgrade might help too...

Why do I need a new netinstall?

I expect a lot of people are going to get caught out by this. I should just be able to consider that I'm using Wireless, not have to remember that I'm using a specific package. Even if this was my day job, I probably wouldn't consider it. (And the list of stuff in the release notes is so gargantuan, it's easily missed.) Fortunately I still had the hAP Lite kicking around, so I've got an AP with the correct configuration already. Others won't be so lucky.

What would have been more useful is if 6.35.4 had big red signs all over anything Wireless to warn that the package was deprecated and about to be removed. I would even go as far as to suggest an interim 6.35.5 release with only that feature would have been a good idea.

Most people are jumping over the versions. Interim version would be for nothing.
Yes, I use to say that everyone should test everything before he does it on productive devices, but even I am time to time possessed by some idea that looks so straightforward that doesn't need to be tested. Then I am tortured and heavily punished by the unwanted side effects...
So. If something works correctly, be glad of it and don't touch it until you test it somewhere. And read the release notes and forum before.

Now the easiest thing is to set the wireless again if the wlan is visible finally.

Why do I need a new netinstall?

I expect a lot of people are going to get caught out by this.
What would have been more useful is if 6.35.4 had big red signs all over anything Wireless to warn that the package was deprecated and about to be removed.

I suggested a netinstall because *you* claim you cannot get it working anymore...   I don't have certainty this is required, as I did the procedure in the releasenote before upgrading.
Sure I expect problems too!   But it is not my business...
There *have* been warnings on the forum for the 6.36rc so those who tested the RC versions already know all about this.
But I completely agree that most people will probably fall in the trap of doing a "check for updates" then "download & install" and find themselves in trouble!
Especially when doing it on WiFi link equipment that is no longer reachable when the WiFi support is not working.

I didn't say I "cannot get it working" - I was limited by time and attention

Somehow the SSID acquired a space inbetween an uppercase and lowercase character (e.g. "MyRouter" would have become "My Router") - no idea how this happened. Maybe I subconsciously added it when attempting to configure wireless-cm2 in the past, and this error was "resurrected" when I switched back to wireless-cm2. Or something. Anyway, removing the space allowed the interface to go into the "running" state, and now all is well.

Many thanks all for your contributions.