Your best action here (if you continue to not be able to get these devices to work) is to open a case with Meraki Support to help troubleshoot. If you are savvy enough, I would try using packet captures to see the exchange between the Associations/Authentication messages to see what may be happening. More often than not when buying inexpensive sensors they tend to use the least expensive parts available and do as minimal tasks possible to try to get a device working (such as versions of OS code, etc).
I would recommend trying to see if it will connect to a SSID without any security or encryption to see if the device will even associate to that. If it does, that is promising as it shows it sees the SSID and is willing to connect. If it won't even connect to the SSID than that might mean there is something going on 'standard wise' where maybe the Meraki AP and the device are just not able to finalize the assocation. If the connection works to this SSID, try changing it by basic encryption such as WPA-PSK with WPA1. This is never going to be recommended real world with the inherent flaws to WPA1, but we are really just trying to find the baseline to this type of device and what it can connect to. I have had some trouble with sensors in the past that will not connect to WPA2 based WPA-PSK networks. From there, see what your results are and then try WPA2. Hoping this helps but really it is going to be around narrowing down what the actual root cause is. Good luck.