Implementing UARTE on a Bluetooth Enabled DK (ncs v1.9.1)

Hello,
im trying to implement the UARTE Driver for simultaneous Use of Bluetooth and asynchrounos Uart TX/RX on a nRF52840 and nrf9160.
The Problem is that neither RX or TX works.

While Debugging i realised it Crashes while trying to create the TXEND Event.
Im getting this Error Message.

00> [00:01:08.938,568] <err> os >>> ZEPHYR FATAL ERROR 1: Unhandled interrupt on CPU 0
00> [00:00:16.987,701] <err> os: Current thread: 0x2000c7a0 (unknown)
00> [00:00:16.993,194] [1;31m<err> fatal_error: Resetting system


relevant proj.conf snippet:
#Logging
CONFIG_LOG=y
CONFIG_LOG_MODE_IMMEDIATE=y

CONFIG_CONSOLE=y
CONFIG_UART_CONSOLE=n
CONFIG_RTT_CONSOLE=y
CONFIG_USE_SEGGER_RTT=y

### Peripheral-UART
CONFIG_SERIAL=y
CONFIG_NRFX_UARTE=y
CONFIG_NRFX_UARTE1=y
CONFIG_UART_ASYNC_API=y
CONFIG_UART_1_NRF_HW_ASYNC=y
CONFIG_UART_1_NRF_HW_ASYNC_TIMER=1

### Enable k_malloc/k_free
CONFIG_HEAP_MEM_POOL_SIZE=2048
CONFIG_MAIN_STACK_SIZE=8192


I think it might have something to do with missing KConfig Options

Any possible Solutions or Ideas would be greatly appreceated

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