Have you ever seen this,video?
Looks as though from the links and info it’s the “Softdevice” that limits due to system resources , memory, tasks #'s too great. Depends on implementation of the stack and availability of memory AFAIK.
I want one Central Android Device (phone app) and 8 “Xiao BLE Sense” Units as Peripherals. Basically 8 notifier’s to one central. Two is a good start for proof of concept though.
https://youtu.be/tbl6Dui-_w4
I know several folks afflicted, my Younger brother has the mask thing too, Your project is very useful and the research is interesting. You ever consider patent it and licensing to other big Co.? Just curious.
Gl 
PJ. 
from Nordic
Yes, the S140 v6.1.0 SoftDevice(i.e. BLE protocol stack) supports up-to 20
concurrent connections and this is a hard limit for our protocol stack.
If you need 30 concurrent connections then I suggest that you take
a look at Mynewt's Nimble stack. It supports up-to 32 concurrent connections
and it supports the nRF52840.
Best regards
Bjørn