OPA320: OPA320

Eric,

1. Some complex circuits will have convergence issues.  Solving these issues is done by adjusting various analysis parameters.  These issues are especially common in high speed transient conditions.  The document link below provides advice on how to adjust the analysis parameters for good convergence.  However, I don't recommend your circuit implementation.  
2. I cannot read the detail in your circuit (the image is blurry).  However, in general a reference buffer is not needed.  The specific requirements of when a reference buffer is required or not is discussed in the ADC TI Precision Labs video series in the "Driving the reference input" series.  In order to know if you need a reference buffer or not I need to know the ADC model and sampling rate.
3. Generally, the reference input of an op amp requires a decoupling / filter capacitor.  The video series above will provide additional detail on this requirement.  When placing a capacitor at the output of an op amp you need to take precautions to assure the stability of the amplifier.  This document provides the method for stabilizing a reference buffer: Reference-Buffer for ADC-Driver.

3201.PSpice for TI Convergence v1.2 3-16-2023.pdf

Best regards,

Art Kay