Importing swim from tcx file gives wrong distance (i.e. none)

Since early March importing a swim from a tcx file gives errors. The time and heart rate come through, but not the distance (says it is 0m). It does seem to have it under the individual laps. I cannot see how to edit it, and if I create a manual entry instead, all the lap data is lost. Is this a known error? How can I fix it?