What Stratux software version are you running? If you're not sure, describe how and when you acquired your Stratux and its software, which will give a clue. Since you mention getting a replacement SD card from AP, does that mean you bought your Stratux from them? (LED behaviors have changed their meanings over time. BTW, there are actually two separate LEDs, one red and one green.)
How do you power your Stratux? Insufficient power can lead to the result you are seeing. If you have changed from a battery to a cigarette lighter adapter, for instance, or changed from one cigarette lighter adapter to another, that could cause this result. (Not all cigarette lighter adapters are created equal. You need one that can provide as much power as possible. Look for 2.4A capability or more.)
Another possibilitiy is software corruption, but if you've replaced the SD card, that would be unlikely.
I'm suspecting a power-related issue.