My mesh network is a mess (or missing)

I am a new user of Homey. Running on new device on version 2.0.2.
I’ve added already some devices more or less only Neo Coolcam devices plus few Heiman smoke sensors. The pairing of the devices went smoothly and many of the devices are paired just fine still, but the range of the devices seams to vary very much.

The devices are all but one battery devices, the exception is the beforementioned, Neo wall switch.

The good:
The siren from Neo keeps the pairing to downstairs in concrete building over, 10 meters.
Next to the siren downstairs is a 240V powered Neo Smart wall sensor. I can “Send basic ON” and off requests getting positive feedback.

The bad:
Other devices, downstairs are not connecting at all.
Despite various attempts it seams that no mesh network is building up. All devices are linked with Homey directly as “Coordinator”.
I have woken them up e.g. door sensor with three pushes. Batteries out for couple of hours… I have tried to bring the Homey downstairs and moved it back up.
I have tried to send Heal commands to the power connected Neo wall touch button, but they have not been acknowledged.

Any thoughts?

ps. that device nr. 5 “Skynjari neo” is listed as offline, but it is working just fine, well connected and reporting.

Try to wake-up the battery-device and then send a heal to the battery-device and to the main-powered device nearby. Then they get to know each other. Worked for me perfectly…

Thank you @bvdbos, I realized after your comment that my wall plug was out of sync with my homey, connected it again, woke up the devices as you suggested and “healed” the network. After this I finally have one using the wallplug as a bridge.

Bothers me a lot not being able to use the siren, which seams to have the best reach, as a connection node in the network. But at least I’ve finally got a step forward, thanks to you!

Offline means nothing more than that it is in “standby” to extend battery life. It only wakes up on triggering motion (or whatever should monitor) or manual wake-up.
Cheapest way of extending the range is put some Coolcam plugs on strategic points.

Thank you @PetervdK, informing. Will add some Coolcam plugs to my setup!