[FortyNiner]

Here's the basics:
'46 Deluxe - bone stock 6V 239 V8 (completely rebuilt 6500 miles / 8 years ago)
2 year old battery with clean connections
Grounds to frame and block with 00 cable
Distributor rebuilt by Third Gen 2 years ago - plug and coil wires replaced
Wiring replaced during restoration to OE spec
New fuel tank and lines during full resto in 2017/18
New radiator / water pumps in 2017 - no issues with heat or overheating

Background
Typically a ready starter after a few seconds of cranking - hot or cold

The Issue
Recently - like just this week - warm restarts are suddenly a problem.
Cranks as it should but doesn't fire. Fuel flow is good.

On the first instance, I used a jump box (after a few minutes of cranking w/o fire) and it started immediately. It has also started instantly if roll starting by popping the clutch in gear.

Today, I found that it will also start immediately if the ignition switch is moved to 'ON' while the starter is engaged.

What have I done?
Checked coil wires and swapped out the coil for a NOS version on hand (no change).
Coil does NOT get warm to the touch when in 'no start' mode
The coil I removed has been sent off to Skip for a rebuild.

Looking for wisdom from those who have been here before. What should I check?

I appreciate any inputs.