Can you confirm that there aren't any supports on that object in the custom supports tool panel? I know the other object has supports in one area.
To work around the issue, I ended up splitting the print into two processes, with support enabled for only that one object. I've used this workaround several times when I've encountered this situation, but it doesn't excuse the developers from fixing it.
The solution is to read my description of the process to get supports exactly where you want them on the first page of this thread, to understand how the process works, and not to expect "someone else" to do all the hard work for you.
The process I described has worked every time for me for something like six years. I learned how the software worked and worked out several way of taking advantage of the way it works to achieve what I want. Restrict the software so it only works one way....and others will shout about bugs as what they want to happen now doesn't!
It would still be better if they renamed "remove all supports" to what it actually does, which is "does not remove all supports but makes you think it did so you get upset when you print and there are still supports, since you expected remove all to actually mean remove all".