Also occasionally it will happen if the rung is made except for one bit, if this one bit is changing fast it does not update on the screen but completes the rung the majority of time.
As paul says, check for duplicate use of output, not very good practice however.
For e.g. I have seen an output written in an Auto section and a manual section, and only one section is enabled at a time but the output will still show on in both.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.