Update 9(10.09.00.74)
Recently in OPPID U9 there has been issue reported by many user regarding Instrument lines when placed are not visible accurately as it is expected typically when using OOTB Imperial workset or project. It appears to be very smaller and not visible to segregate it as Instrument Lines or Process Line..When the same instrument lines are placed in Metric Workset it appears to be normal and visible as shown below.
Place new Instrument Lines for which changes were done and the Line will get reflected properly as it is in Metric project. Thus proper visible instrument lines get displayed
If above problem still persists, then please create a Service Request and contact the Bentley Product Advantage group. Please include a list of all relevant details to get in depth analysis for a solution or workaround