when you make a direct fc Connection the port mode is changing from pp ( Point to Point) to arbitratet loop (AL). Please check is your hba is still supporting this and that the config settings on the AIX side are correct and allowing the hba to go into arbitratet Loop mode. AIX can be very tricky.
Also check which version of driver you're using on the host HBA - if this is based on an Emulex chipset, you may need to use an older version - we've seen issue on ESX 6.5 and direct connect at 16Gb and the new Emulex driver does not work (it gets installed when you upgrade to ESX 6.5). Installing the older driver fixed the issue.