Is your field a multiple lines of text column?

yes

Have you set the field "Append Changes to Existing Text" to "Yes" in the configuration of this column?

Yes and it's plain text. Should I make it rich text?

I've tested in my environment and the workflow doesn't start only if I enter a comment which is exactly the same as the previous one. The workflow starts if I don't add any comments (as null is different from a not empty string).

I think that you should configure the following conditional start :

Start when items are modified and : Status Comments Is not empty

Hope this meets your needs

I've occasionally had issues with conditional startups, and what has been working for me is to add a 'pause' action at the beginning of the workflow (for 1 minute). I haven't had any issues since I started using it with conditional startups.

Emily, I had a very similar situation earlier this week, except that my workflow kept running twice every time an item was updated, rather than just once. I spent hours trying to figure out why, until I realized the culprit was a multi-line text field with Appended Changes enabled (as Caroline Jung suggested). There may be a simpler way, but this is how I resolved it.

• I created a column in my form called Comments Added Flag
• I added a rule on the Comments field to set the flag to Yes if comments are entered
• Back in my workflow, I changed the condition to be If Comments Flag = Yes
• As the last step of the workflow, I reset the Comments Flag field to be empty

That stopped the workflow from running twice every time the comments field was modified.

so navigate to the list or library you want the workflow on.  Select workflow settings > Create a workflow in nintex workflow.

Choose blank template and click create.

Click workflow settings in the ribbon and define your starting behaviour here: