Lines appearing during ironing
There's a couple of Cura settings that can help, that I know of:


In the 'Travel' section, change "Combing Mode" to "not in skin". Combing means it tries to move the head over areas that have already been printed. This is a good thing most of the time, but if it does it while it's ironing, it will make an annoying line. (I am not sure why this isn't automatically turned off for the ironing pass, but it seems it isn't.)
After enabling ironing, an option "Ironing Pattern" appears. Try changing this to "concentric." This produces a different pattern, which you may or may not like, but it seems less susceptible to those kinds of lines appearing.


Here are some other settings that might help. I'm suggesting these on the assumption that some of the lines are caused by the print head travelling over the ironed surface, which is what it looks like to me from your photo. I got them from this Cura documentation page, but it doesn't mention ironing, so I can't be completely sure whether they will affect the ironing step.


"Avoid printed parts when travelling" - this might help a bit more than just turning off combing, since it will try to go around the printed areas instead of just cutting across them. Apparently you have to enable combing for this to work.
"Z hop when retracted" and "Z hop only over printed parts." This should make it lift the print head up when it can't avoid crossing the printed part. It may be that you have to enable retraction, combing, and/or "Avoid printed parts when travelling" for these to appear.