Arduinos unstable random freezing and messed up serial output??

hi guys 1 doing head in.

i have project involves having multiple arduino nanos connected each other via softserial. have been connecting pc them @ same time via usb , selecting each serial port number upload , test code. has worked fine while , have been uploading testing , switching between arduino connections via serial usb no problems.

but yesterday ran , without changing of code started noticing debug serial output showing garbage characters , big gaps of space @ random. hitting reset button had varying results. random io pins turn one. pin 13 led may stuck on. have button may or may not register me pressing it. 1 device work bit wouldn't , vice versa. on place , extremely unstable.

i thought maybe somehow there problem serial communication getting corrupted when uploading , viewing output. have tried different usb ports on pc , replaced cables , usb hub not change.

what going on?

without seeing program(s) can tell?

if have more 2 nano's connected @ same time please make simple pencil drawing showing how connected , post photo of drawing.

have common gnd connection between them all?

...r

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