Android Question Bluetooth example t (CRLF) his is a test

Are you using prefix mode (see AsyncStreams tutorial)?

no prefix..
Now I added a space and sent " this is a test" and the result was
:
: this is a test.

So the space resulted in a CRLF then the complete sentence without a space. This means to me
that the incoming data is coming like this:
1- the first character whether it is a letter or a space
2- CRLF
3- the rest of the string

example 1:
I send "testing". the result is:
:t
:esting

example 2:
I send (Space)testing. the result is:
Space)
:testing

You should not assume that messages sent from the PC will arrive as a single message on the device. This is exactly the purpose of prefix mode.

However if you cannot use prefix mode then you can use AsyncStreamsText (assuming that each message ends with an end of line character).