Strange behavior of the DALI controlled luminaires
DALI requires less than 2V maximum difference between the highest and lowest points on the line. To achieve that you must use sufficient cable gauge and a power supply with sufficient current limit. The luminaires will go on "spontaneously" if they see a system failure condition, which is less than minimum DALI voltage for more than 500ms. For up to 150m you need to use 0.75mm squared CSA.

You may be overloading the PSU in the 905 router. Although it has a current limit at 250mA, which is the maximum allowed by DALI, you have 48 luminaires plus 3 control panels. The luminaires (assuming one DALI driver per luminaire) are restricted to 2mA each by the standard, but the control panels do not have the same restriction; they are allowed to be up to 250mA each (although not a good idea to go that high). So measure with a current meter in series at the router end what you are drawing during non transmit times, and look at the DALI signal with a scope to see if the high levels are dipping below 9.5V.