Reduncdancy, Reduncancy, Redundancy.
I've probably had one or two lockups over the years I've had an apex. If I had to guess, all of the reconfiguration of your system caused you to bump the aquabus connections which could have led to a bad connection.....check them out....then go to this address on your apex.
http://whatever.apex.ip.address/cgi-bin/abdump.cgiManually refresh that page occasionally, look at the ecount column. If a device is taking errors, then you need to look at that cable. Although I had to have neptune tune my aquabus a long time ago. My display does normally take some errors.....but I believe this is fairly normal.
What was your firmware version? The version 4.30 is out, and has been very good for me. I would upgrade to the latest version in any event.
1) Use the backup power supply on the base module. This allows provides a secondary power to the CPU, vs just the aquabus. There are also separate power fail alarms.
2) Use a 3rd party monitoring service. (I use Reeftronics) This is a very simple logging server, but it will send you an email alert if your apex does not respond.
3) On your heaters, make sure to use a heater with an internal temperature control, Set the heater temp to just higher than you want your tank temperature. Then use the apex to control the temperature. Set the Fallback condition to your heater Outlet to ON, In the event of a communications problem with the base unit, there will still be heat.