UART Rx hangs after a few seconds when BLEPeripheral.begin(); is called on nRF51802

[doh38]

Hey,
I hope to get some help there... getting grey hairs ^^
I have a nrf51802, got it to work nicely on UART at 115200 (cannot use lower)
Anyway, as soon as I start the BLEPeripheral, the RX will work (totally) randomly for 10-->360 messages (at 50ms) and suddenly stops/hangs for ever. The nrf works, Tx works too... just the buffer not being "populated" it seems.
I checked the uart and ringbuffer libs and it seems that the RXD interrupt is triggered, but the delta remains after at 0. and therefore.. well not available.
I also tried to stop the Serial after the rx stopped to respond by calling Serial.end(); and it instantly crashes the code.
This is a bit very deep code for me. I must admit having absolutely no idea where the problem could be.
*if that may help, I tried a while ago to set the UART at 9600... and in this case, it was working.
I tried (without success):

• increase buffer size
• increase read speed
• change uart irq priority
• remove all the rest of the code

I really hope to get a bit of help there, I have no idea where to search anymore.