BLE communication is too slow and crashes on timeout

How does it work in the sim?

Are you using notify, or are you just reading the characteristics? With some characteristics, notify is based on time (you get notified every x seconds instead of when things change)

for example, the Air Quality on the thingy52 only notifies every 10 seconds by default, but it can be changed to every second or every minute if I recall.

I suspect the issue isn't with the watch, but with the other end.

Another possibility could be is your sensor is sending data too fast and the watch can't keep up.

If you can't run in the sim, the Nordic dongle that works with CIQ is $10-$15 US and believe me, well worth the cost as you can debug right in the sim without doing sideloads all the time.  It will pay for itself in an hour!

In simultion, scan is little bit faster then on watches, but reading is slow too.

In this iteration i'm using request read method. specifically I do this:

->start application
-> start scan 
-> waiting for start scan done (onScanStateChange)
-> placing scan results to array (like in nordic thingy example, but without filtering anything)
-> select Scan result (from gui)
-> set scan off
-> waiting for scan off done (onScanStateChange)
-> pairing with scan result
-> waiting for connection state change handler
-> geting service and characteristic object from device object
-> requesting characteristic read
-> waiting for characteristic read handler
last two steps are in cycle

For debug im using nrf52-dk

i was tested device (bm71 module on my device) with nrf connect app, and with microchip connect app on cell phone. This side is working really well. There is minimal latency in manual reading, even in notified readings (it works with few milliseconds latency)

How often are you trying to read?  is it based on a timer?

A couple of things that occured to me.  After you get the onCharacteristicRead(), are you doing somthing like a Ui.requestUpdate() so onUpdate() is called to update the display?

And when you communicate, are you using a queue?  You can't just read characteristic A, then characteristic B, and have both work.

you need to do something like 

read characteristic A

wait for the onCharacteristicRead() then

read characteristic B

Another thing I do in my apps is I set a timer when I do something like a read.

If the timer expires before onCharacteristicRead() is called, I consider the connection dead, disconnect and reconnect.

kind like timer, i have timer with 500ms period and in callback i'm waiting while last read is done. After that i request next read.