Uno+WiFi Shield: sometimes not able to read returned HTTP data from client

Here is a sample output:

Just received signal from device #: 100002371
Time to push!
HTTP/1.1 422
Just received signal from device #: 100001280
Time to push!

Just received signal from device #: 100000367
Time to push!
HTTP/1.1 422
Just received signal from device #: 100002371
Time to push!
HTTP/1.1 422
Just received signal from device #: 100000367
Time to push!
HTTP/1.1 422
Just received signal from device #: 100002371
Time to push!
HTTP/1.1 422
Just received signal from device #: 100001280
Time to push!

Just received signal from device #: 100000367
Time to push!
HTTP/1.1 422
Just received signal from device #: 100002371
Time to push!
HTTP/1.1 422
Just received signal from device #: 100001280
Time to push!

Just received signal from device #: 100000367
Time to push!
HTTP/1.1 422