Siglent SDS1102X Serial decoder not decoding properly

[janoc]

Before you reject the Saleae...

The OP wants to see an analog signal related to the decoded data (which seems to be a firmware state indicator) so any kind of logic analyser isn't going to work for the problem at hand.

AFAIK, the Saleae has an analog input too:

Specification for analog use:

Sample Rate: 50 MS/s @ 12 Bits
-3dB Bandwidth: 5MHz (signals with frequency components above this will not appear right)
-10V to +10V voltage range

https://www.adafruit.com/product/2313