I can reproduce it. First, without trying, I thought it was a depth issue (something occluding the text).
But it’s not the case. I believe it’s some kind of memory / buffer limitation.
The good news is that for me it works by doing this:
textLayer.textFont(createFont(sfont, mainFontSize, true,
new char[] {'C', 'a', 'l', 'i', 'f', 'o', 'r', 'n'}));
So I limit the character set and that makes it work.
BTW. I’m using a GTX 1060. I’m not sure an integrated graphics card could handle 6000x4000.