I am sorry you had breathing issues and were not feeling well before the event. I know how frustrating that can be. So much of events and races is completely out of our control. Something similar happened to me last Sunday. I was doing really well riding with the front group/fastest group of guys in a gravel race (even got the QOM for the race) when a nasty crash happened inches ahead of me. I was quick enough to swerve into the grass and avoided it. But by then the group split and I was solo. That was 14 miles into the 62 mile race. At mile 35 I started having stomach cramps that got progressively worse. Debilitating actually. Saw all the other women zoom past me. Had to stop several times to decide if I could continue on. Then at around mile 50 I started to have cramps on my left leg. I haven’t seen the results yet but I probably finished DFL. I had some sort of stomach illness, because I was sick for hours and could not stomach anything.
That is exactly why we need to love the process, the every day of training, the weekly rides, and not be attached to events or outcomes. No expectations, no attachments. Knowing you are giving your best every time you are on the bike is what makes us winners.
More specifically to your situation, @Gossimrr, do you have asthma? Do you use inhalers? Also, how do you know you were above your lactate threshold?