The issue has been resolved. Thank you again for the advice and ideas to check.
I felt that the issue seemed to be heat related, due to it seeming to happen primarily while processing MDF doors (longer processing times between tool changes) and on days when the shop was really warm. I could run though 20-30 sheets of melamine in a day without issue on a nice day. I could run a couple sheets of MDF doors and it would present itself. If the shop was 85-90 degrees like we had a month ago, it would present itself.
I hired a local CNC service company to come look at the issue after talking it through with them. After they checked out the air valves above the spindle and various other ideas mentioned here, they removed the plastic hood at the top of the spindle to begin a deeper look and discovered a broken bolt at the top of the spindle. There are 4-M6x135mm bolts at the top of the spindle and one was broke at the top of the threads. The plate these bolts are holding down would move ever so slightly (less than .5mm) at the corner with the broken bolt with each manual lock/unlock cycle. Replaced all 4 bolts and so far we are working without issue.
The theory is this movement prevented the draw bar from dropping fully (primarily after longer machining cycles when the spindle/tooling/cone was warmer).
I would love to know how that bolt would have broke. The tech thinks it may have shipped new that way. The previous owner never experienced this issue, but he processed closets only and would have been using the drill block and cutout tooling only with minimal tool changes.
Wish me luck!