Acer Nitro 50 N50-600 with i7-9700 : Ram issues when going beyond 32gb

Unholy

Hello guys,
I bought this PC second hand, it came without a GPU, so I put the Radon RX580 that was in my previous PC.
It also only had 1x8gb ram stick, that I tested. I had on hands 2x16gb ram sticks, and decided to purchase another 8gb of ram of the same brand as the other 8gb, for a total of 48gb of ram.
Even though I thoroughly tested both 8gb sticks of rams, when the 2x16 are installed, when I add one 8gb stick of ram or both, it only recognize 32gb or ram...

In terms of how they are positioned, starting from the CPU, the first 2 slots are occupied by the 2x16gb, and then the next 2 by 2x8gb.

Is there anyone who have an idea of what is going on? Anything I could try?

Thank you very much for taking the time to read my message. Have a good day! 

Leostat

What are the timings and speed of all the sticks? It could be the board doesn't support more than 32gb, or it could be incompatible sticks, or it could be that mixed mode isn't supported

Does it work if you pair a 16gb stick with a 8gb stick?