Both of the systems are mechanical. No lcds or computers.
The softener kickoff happens so infrequently (I bet once a month, and it happens based on how much water has been used), that I don't think it's the issue, since I've already had flooding twice this week. Plus, the softener does its thing later than the neutralizer. I 100% guarantee both systems did not go off this last week when the system flooded twice.
I do feel, though, that your general assessment appears correct: the system can't handle the load at times. The question is why now? Has a small enough blockage occurred somewhere recently, and that's why I have an issue only when the neutralizer goes? I see no evidence whatsoever of any issues of backup during daily water use.
It seems what I have to do is have a plumber come in first and make sure the drain pipe in the house is clear and adequately sized. My guess is I'm going to get a pass on that considering it's a straight, clear shot out the back of the house.
Assuming that checks out, septic people are the next call. They can hopefully give me some insight as to whether the system has some sort of problem that only rears its ugly head when the neutralizer does the backwash (and why for 11 months I've had no problems, and only recently there's been an issue).
The thing that's frustrating, of course, is that I expect every 4 days to clean up a flood, and my concern is perhaps the flooding will get worse as time goes on, so I have to stay on this problem so it gets fixed ASAP (and historically I've had trouble getting people to respond promptly and keep their appointment).