3Ware RAID6 array sometimes hanging. Undetected broken disk?

2 things that were not brought up so far:

1. Is this a SATA RAID controller? If so, SATA cables are prone to aging and replacing them might solve such issues easily. Most of the time this can be tried when disk errors, lags, timeouts occur but the SMART values are all ok and the drive passes all self tests. Unfortunately finding a good SATA cable vender is difficult.
2. 3Ware RAID controllers are old and unsupported these days. You will neither get firmware upgrades nor spare parts. In case your controller dies the RAID might be unrecoverable without the matching controller AND firmware. An expensive data recovery is then needed.