there is never, ever, a valid reason for have a non-linear x-axis in a chart
Agree ... but the x-axis is linear ... since it is not about time, but about data point / Visits ... the time between two visits is irrelevant in this case.
Acc. to you, (assuming that the unit is 4 weeks) the scale between : - Screening (week -8 [it was -6 in some cases]) and Week -2 - Week -2 and Week -1 - Week -1 and Week 0 - Week 4 and Week 11 - Week 11 and Week 12 are wrong ... 4 "scales" were used (1, 4, 6, 7 week(s)).
Meanwhile the scale was based on the # of the Visit and the scale is 1 (in every cases / Visits)