What technique is more suitable for multiple (10+) simultanious bluetooth communications? CC2564
I feel you are trying to overstress the BLE architecture. An attribute send each 50ms from 20 nodes would need a central with a connection interval of 2.5ms. Too bad that the minimum is 7.5ms (exactly six 1.25ms ticks)
I think you should review your bandwidth need and maybe use another kind of protocol.
This of course if the master actually support 20 connected nodes. When transmitting data in the advertising protocol (i.e. as a beacon) the limit goes up to 20ms but it's quite possibile that some conflict would happen: the idea is that even if one advert is jumbled the next one will more or less arrive correctly (but of course the air will saturate)