GC752X Switch Login Failure

I have a curious issue with the GC752X switch.  After running for a while, the switch seems to lock up and will not allow any further logins.  We have all the switches on a separate Management VLAN.  We have one connection from a Linux server using FireFox that the technicians use when making VLAN changes to the switch.  A few of the technicians also connect using a separate VNC session on the Linux server to the switch using FireFox as well.  When the issue occurred with one of the technicians, I tried from my own VNC session and could not get in.  I could ping the switch.  I could access it and get a login screen but when I entered the password it would give me Login Failure.  So I accessed the VNC session that the technicians share for VLAN configuration changes and it would let me login fine.  There was not an issue with the password.  

I checked the Linux server and there were about 10 VNC sessions with connections to the switch.  I disconnected those sessions as I was told sometimes when there are too many connections to the switches they get the Login Failure issue.  I was still unable to login and kept getting the error message.  I stopped and started working on another issue and came back to it after about 2 hours or so and then I was able to connect.  

The next day another technician had problems again getting the Login Failure error message and he simply rebooted the switch and was able to get in again.  

Is this common?  Has anyone else seen this issue before?  Any ideas how we can get around this issue?  We run space flight simulations that can last days or weeks at a time.  Flight systems need constant communications with each other at all times to remain in sync with each other.  We cannot afford to be rebooting switches when they start acting up.  

Model Name      Boot Version    Software Version

GC752X             B1.0.0.4           1.0.5.25

Thanks