Hey @████████- if you are still having this issue...
I'm seeing the same thing happening (see my post).
I feel like there is a bug with the system saving the selected field widths when there are six or more items in the row, and instead reverting back to equal field widths.
Obviously, the bug needs to be fixed. But in the meantime, I've found a workaround that appears to be working consistently.
Once I have my six fields in the row, I change their width so that fields 1-5 are all as narrow as they can be, and field 6 is as wide as it can be. Then I save changes and leave the page. When I return to the page, the widths have now finally saved to what I set them at instead of reverting back to equal widths. I can now set them to what they need to be and save it, and it seems to save consistently at this point.
Note that if I reposition any fields in or out of the row, I have to do it all over again.