It is not related to texture but the Backward compatibility to BMFont that created with NGUI before the v1.84
Since I use the free version (v 1.68b) to build my game first, after I build most of the UI layouts, I brought the paid version and upgrade the code base directly without recreating the Font Asset and Altas, The problem is v1.68b BMFont Serialize 65536 BMGlyph to the asset file, but in v1.84, it populate the old data to mSaved and mDict, so it got hangs when startup
I recreated the existing font asset and fixed the problem, but it took me a whole day to locate the problem