How far apart are AP-A and AP-B, and what is in between them? Beside walls/windows, is there any machinery, AC/heating, florescent lighting?
Are you running Solo AP code on the APs, or controller managed? (different troubleshooting tools)
What kind of mobile device is it? Are you running latest radio drivers?
What kind of application is it running? How do you know when it is offline sometimes?
Does it happen to all mobile devices, or only one certain kind?
