I ran into the same issue, without any resolution: Intervals.icu messes up fit lapdata - #10 by Jaap_van_Ekris
My solution is simple: the upcomming version of OpenRowingMonitor will be able to present all data by itself, without use of intervals.icu. RP3’s portal also allows uploads and it responds well to C2 data. But it is a paid portal (but these guys know how to handle rowing data very well).