This answer is probably no longer of relevance to you, but perhaps some other reader will stumble upon it as I did.
The problem is that you don't have a timestamp in your scripted output, so Splunk goes looking for one.
Both values for MaxMemory and TotalMemory appear to Splunk to be valid epoch-relative dates, but I'm guessing that 1908932608, which maps to 29 Jun 2030 03:03:28 GMT is too far in the future.
Then it sees 1130823680, which maps to 01 Nov 2005 05:41:20 GMT
Every time your script runs, there is likely a slightly different value for TotalMemory so that computed time is going to jump around, as you've experienced.
One way around it would be to add an explicit timestamp at the beginning of the line of output.
Another would be to disable the timestamp processor for this input so that it would get a timestamp that matched the time the input was received
DATETIME_CONFIG=NONE
See Disable timestamp processor for more info on the latter.
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