433 MHZ connection between two Arduino (nano,uno) fails after some time
Regarding the hardware problem, there are some advices in the comments.
As you wrote, the solution is to reduce the bitrate at 2000 bps.

The remaining question is why the receiver always truncates the message (after a receiving error occurs). The answer is in the definition of the buflen parameter of the vw_get_message function. The page https://www.pjrc.com/teensy/td_libs_VirtualWire.html says:


  "buflen" should have the array's maximum size upon input, and upon return the number of bytes actually copied is retured.


Therefore, when a transmission error occurs, the buflen variable returns a smaller number to inform you how many characters are received. If you do not reset the buflen variable to VW_MAX_MESSAGE_LEN before calling vw_get_message again, you are telling the library that you expect a smaller number of characters and the function respects that size (thinking that you have a smaller buffer).

In other words, if you want try to receive the full message after a transmission error occured, set the buflen variable to VW_MAX_MESSAGE_LEN before each call of the vw_get_message function.