Believe it or not I had this in my sketch....

pinMode(A7, INPUT);

It appears this was the culprit all along .....

Sorry for ringing alarm bells..

I have spent the last 2 days trying to figure out why my SoftwareSerial port signals change from nice clean square waves to horrible dirty pulses with a slow decay and not reaching 0V.

I have discovered that RemoteXY_Handler is using a HUGE amount of memory, and as your sketch gets larger, it tramples all over your variables, probably its own as well...

My own figures indicate that a moderate interface with 12 input variables, 13 output variables (3 of which are Strings, lengths 27, 41, and 21) eats a massive 1060 bytes of free memory !! and in doing so is affecting my SoftwareSerial port timings.

I don't have the skills to dig into RemoteXY library code to see what is using it all....

Here's my figures:

Prog Mem : 10752
%age : 35
Vlobal Var : 987
Free for Local Var : 1061
SSerial OK : YES

Prog Mem : 11076
%age : 36
Vlobal Var : 989
Free for Local Var : 1059
SSerial OK : NO

If you get issues that aren't explainable, it's probably RemoteXY trampling all over your memory !!!