I don’t think you hit the limit, but using bulbs as routers is tricky. Apparently (based on my own experience, and similar experiences from other users), bulbs don’t do a great job as routers as they don’t route every message. On the other hand, some devices are very picky when selecting a router (see other messages on this forum).
My recommendations: try adding the devices when they are closer to your coordinator. I know it’s best practice to add the devices in the location where you will be using them, but if there is no suitable router nearby the pairing will fail. If the devices don’t show up, try to re-pair, and re-pair again until they are visible in the zigbee2mqtt logs. For some devices, you might have to re-do this 10 times before the binding is successful. And if required, add some more routers (such as smart plugs). If you notice that the network is unstable, remove all bulbs (and add them on a separate network, with bulbs only).
I also noticed that adding devices is easier when you -temporarily- configure allow_join to true in the zigbee2mqtt config, instead of using MQTT messages for enabling this. Just don’t forget to remove this setting again when you are done.