Shell script silently exits. Why?

[Pavel A]

Dear experts,

We have a strange problem with ash script: the shell silently exits while executing a script. It is likely caused by a "let" command. 
Anyone seen similar behavior? How to debug it?

Busybox version is 1.22.1 (this is what it prints out, not sure about configuration and build details). 
The same script works well on busybox 1.16.0 
Unfortunately this does not reproduce on small example. 

The failing place in the script looks like;
Somefunc() {
 local v
 echo "this prints"
 let "v = $foo & 0x000FFF "
 echo "this does not print"
}

We checked that the script does not contain weird unprintable characters and other obvious things. Just plain ascii. 

Best regards,
pavel_a