Are there any good sources for tactics used by John Hunyadi and Matthias Corvinus? I have found some magazines, but that's it.

Related: John Hunyadi appears to have used, and had success with, tactics which included wagons in the battle line to protect flanks of the infantry from cavalry charge, while also forcing Ottomans to deploy Sipahis on the flanks. But from what little I had been able to find, Matthias abandoned these tactics and instead employed circular schiltron to shield his cavalry, which would counter-charge from within the schiltron. So what changed?

I would say first of all look for sources on the Fekete Sereg / Hungarian Black Army you might have more luck. That is a fairly popular subject in military history circles, more than Hunyadi or Corvinus himself arguably.

The main victories won by the Hunyadi / Corvinus family against the Ottomans using the war wagons that I know of were two engagements in the 1430s and at the Battle of Nish in 1443. Jan Dlugosz talks about some of these battles if you have access to his Annales, that is a great source. I think Anneus Piccolomini mentions them as well.

You might also want to look into the Hungarians use of armed gun-boats, which were critical to Hunyadis victory at Belgrade in 1456. Apparently he had hundreds of heavily armed ships, barges and boats, which were similar to the wagons except... floating. They were able to keep him supplied and interfere with Ottoman river crossings and so forth.

My guess as to why Corvinus may have switched to pike squares later on would be that most of their war wagons (and about half of their cannons and firearms) were manned by Bohemian mercenaries, mostly Hussite heretics. In the 1460s Mathias Corvinus joined a 'Crusade' against Bohemia and went to war with the popular Bohemian King "George" of Podebrady. This may have stripped away some of his Czech and Moravian support.. I think he also had a falling out with Jan Jiskra, the mercenary captain who controlled a lot of the Czech mercenaries in the hills of Northern Hungary (what is now Slovakia). So he may have just lacked sufficient manpower that was experienced in the war-wagon fighting techniques by say, 1470.

I do know that Bohemian mercenaries were still being employed all over Germany with their wagons through the end of the 15th Century, and their use didn't decline until the Landshut War of Succession, when Ludwig von Eyb defeated a large group of them at the Battle of Wenzenbach in 1504 using Landsknechts and wheeled culverins. I think Wenzenbach means 'wend river' or something. Wend being a German name for Slavs.

War wagons continued to be used in the East though well into the 17th Century. The Cossacks adopted the Czech style tabor and the Russians had their own version, the Guliai-gorod which they used successfully against the Ottomans a few times.

Here is an article on that

https://brill.com/view/book/edcoll/9789004221987/B9789004221987-s006.xml

This was a battle in which the Muscovites used their version of the war wagon successfully against the Tartars / Mongols

https://en.wikipedia.org/wiki/Battle_of_Molodi

The last page of this forum topic on pavises has several quotes from Hunyadi and Corvinus, plus pictures of Wenzenbach (also called Schonfeld or Schonberg)

Although brief, this article on SHIELD_OF_MATTHIAS_CORVINUS_ARMY_LATE_MEDIEVAL_INFANTRYS_TACTICS_IN_CENTRAL_EUROPE_" target="_blank" class="postlink"> The pavise of Matthias Corvinus army has some useful info.

Jan Dlugosz describes an incident during the Hungarian-Bohemian war of 1468-1478 (i.e. the 'Crusade') where George of Podebrady is in a valley with a big Bohemian army consisting mostly of infantry on war wagons, while Mathias Corvinus is in the surrounding slopes with a larger force that is mainly cavalry, mostly light cavalry. Podebrady can't get his wagons up into the hills and Corvinus won't come down to face the wagons, which Dlugosz says have 'scythes' on the wheels. So it's a standoff. At one point Podebrady, who was an old and fat man by then, offered to fight Corvinus in single combat, but he declined.