Ok, I just found a bug with mem watcher 12.3.
I am using Snes9x 1.51 v5.1, I got the "target" line from that new Snes9x feature and paste in the s9xwcnf0.txt.
But S9xwatch wasn't showing any memory addresses and their values.
I found the reason of that, it is caused by some conflict with an other "target" line.
The "Target" for Snes9x 1.51 v5.1 is:
:target:snes9x.exe:70F1B0:0024:002C:0034:B165:B17C:72FDF4
And the "Target" line that is causing troubles is:
:target:snes9x.exe:70D350:0024:002C:0034:B14E:B17C:72DF94
Note that there are many similarities between them and I guess S9xwatch just got confused to differenciate them.
Yes, the line could be disabled and reenabled when it will be needed or, a better solution, fix the code to compare one line to another so it's 100% reliable. Because I guess the current code only compare part of the line with others.
But my intuition tells me that the ":snes9x.exe:" is maybe the problem.