How big is your spreadsheet when you cap it at line 2954? Maybe something near a power of 2?

Since Excel file format might not be line oriented (I see lots of unpack statements in the parser source), the limitation might be in bytes. Do other excel files stop at exactly the same line ?

You might edit some lines in the spreadsheet to be much smaller and see if this lets you see more lines. If yes, then there might be (for example) pointers/numbers of double length in the spreadsheet that the parser doesn't know about or just calculates wrong.