If item is configured only with scheduling intervals and scheduling interval delay is more than 5h, then graph line for this item becomes dotted.
This happens only if data is from trends.
If item have at least one scheduling interval and if update interval is 0 and item have no flexible intervals than item line should be drawn as trapper item.
Same issue was described in
ZBX-10789 however it didn't fix case when data is from trends.