I have had this issue for a while, after upgrading to a later version of the firmware. Older WinCE clients on 2.4GHz seem to drop off the network and do not come back. This only seems to affect T300 APs, that's the only outdoor APs we have. Our indoor APs (R650 etc) seem not to be affected. The clients are barcode scanners with Sumit WiFi cards that are old but not likely to be replaced very soon.
220.127.116.11.1038 seems to be OK. But anything later causes problems.