Trouble starting sometimes when warm, but rarely when cold. Newer battery load tests OK. New starter, new alternator. Help!

Replace the igniter and coil. Apply silicone heat transfer compound to the back of the new igniter.

Any chance this could be related to the Main Relay?

Yes. Main relay problems, however, usually appear in the heat of summer. Main relays are not affected by engine temperatures but inside cabin temperatures.

The Main Relay is suspect because an arcing smell appeared early December. Also, we did see similar cases online. Thanks so much for your time and interest. Merry Christmas, Marjo

In that case, I would replace it too.