Buffers down to 128 samples and still getting bad delay in guitar track...

I've recorded eleventy jillion guitar tracks and never had a problem like this.  I'm sure it's just some stupid thing I've forgotten or I'm not thinking of...but even though I've got my Audient iD4 set at low latency and 128 samples I'm still getting very serious latency delay when trying to record a guitar track in a current project.  Have both record and input monitoring engaged so I can hear GR5 or Amp4, etc...tone but the delay is too long to record with.  My short term solution was to just the record the part dry and then effect later.  But that's not a real solution at all.  Anybody have a guess what I'm forgetting or not doing??
 
Geeze Louise.
 

I've hit that wall a few times myself. I tend to try and strip out anything non essential untill all tracking is complete. I've gone so far as to render a rough mix and send all tracks into archive just to relieve processing chores.

I'll 3rd that. I always forget to bypass them and bingo. Midi is even worse. 
 
128 is a reasonable buffer but what counts is what Sonar is reporting to you in preferences as your Total Roundtrip Latency. Example mine shows as 20 ms which is enough to throw me off. I've never had a system that could work with Guitar Sims as the lowest RTL I can get is around 12ms but then everything grinds to a halt. 

musicroom
Sometimes I have plugins on a bus or master that I forget about. Voxengo Curve Eq has got me a few times.

Yep - some of these plugins -and- to the reported latency, because you're using PDC (plugin delay compensation).

Try disabling plugins until the latency gets better.

(Reaper actually reports this for individual plugins - so when I'm set for 64 samples latency, some plugins drive it up to 128)

Click the PDC button on while tracking. This takes care of (I don't know how) plugs in the master that have large delay.

Howdy! Whenever I have this problem I light up the PDC button in the toolbar MIX module. The doc says: Temporarily bypass all inline plug-in delay compensation (PDC) effects in order to avoid delay compensation induced latency while tracking virtual instruments or input monitored tracks.
 
Usually does the trick for me. Hope that helps you.