nrf9160 uart shell echo works on nrf9160dk (SICA B1 2110AM) but not on Thingy91 (SICA B0 1924AP)

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I have two boards, a Thingy91 with "nrf9160 SICA B0 1924AP" and a nrf9160dk with "nrf9160 SICA B1 2110AM". Everything works as expected on nrf9160dk but on the Thingy91 shell echo do not work (i.e. keys pressed in console not visible until I press enter).

it seems that `nrf_uarte_event_check(uarte, NRF_UARTE_EVENT_ENDRX)`, which reads the `ENDRX` register, behaves differently on the two boards. On nrf9160dk it returns for every character received but on Thingy91 it does not return until new line.

Is this a known issue or am I missing something obvious? I have compared .config, .dts and uart register values but found no clues, except that some `RESERVED` uart register have different values between the two boards.

Some relevant configs:

CONFIG_UART_INTERRUPT_DRIVEN=y

CONFIG_UART_ASYNC_API=y

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Board versions are:

- thingy91 PCA20035, 1.0.0, 2019.52, "nrf9160 SICA B0 1924AP"

- nrf9160dk: PCA10090, 1.1.0 2022.4, "nrf9160 SICA B1 2110AM"

Possible related errata?: infocenter.nordicsemi.com/.../anomaly_160_23.html

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Tested with nrf/samples/nrf9160/at_client. Interesting! Same behavior on both thingy91 and nrf9160dk - no echo. Is this expected? i.e. the app assumes line buffering on "the other side"?

Also tested on another Thingy91 - same issue.

Battery voltage is 4.1 V.

Some observations that might provide a clue:

```

promt:~$ <-- cursor should be here 

<-- but is here on next line 

``` 

Output _sometimes_ cropped. Example entering `123456789" and then enter, output is:

```

promt:~$ 1234567 <- should be 123456789

123456789: command not found

```

I guess it is related to uart fifo size?

(btw. standard markdown support on this site would be nice :) )

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I received a newer Thingy:91 today, v 1.6.0, 2021.19, and echo works on this one!  So it seems likely it is related to the Connectivity Bridge. How do I check version and upgrade Connectivity Bridge?