I attempted to link summon S:P Little Knight using the Bearbrumm and Kerass as seen in the picture. Little Knight was lit up in the extra deck, implying I could summon her. I began the summoning process, but the game would not let me select Bearbrumm as material.
I then attempted to Xyz summon Gigantic Spright which was also lit up and should be legally summonable. The same thing happened, I could begin the summoning process, but could not select Bearbrumm, forcing me to timeout and lose as I attempted to force the summons to go through.
I was under the Tri-Brigade “you can only use beast/beast-warrior/winged-beast as link material” lock, but that shouldn’t be relevant for Gigantic Spright, and both my monsters fit those types anyway.