Script suddenly stops working but works in other sheets

Question

Been using getFileById & insertImage in a sheet/program for months with no problem but it suddenly stopped working two days ago. In order to solve the issue I created a fresh sheet and did this simple code:

function myFunction() {
  var picId = "1x2jkgSQvVKAIOg6DQ0rss82YhTQl918c";
  var picToPlace = DriveApp.getFileById(picId);
  SpreadsheetApp.getActiveSpreadsheet().insertImage(picToPlace,1,1);
}

It works just like it should however if I stick the same code into my main sheet I get "Exception: The image could not be inserted. Please verify it is valid and try again."

Why is this happening? I'm not doing anything different, the function is sitting by itself. Been building this sheet/program for months. Have I overloaded the sheet somehow? Again, if I make a fresh, plain sheet, stick this code in it, it works fine, but if I go back to my main sheet, stick in the same function, it just refuses to work. Its in its own function, nothing else is happening w/in it, it's the only thing I'm calling. I'm at a lost trying to figure out why insertImage has completely stopped working in this sheet. There are thousands and thousands lines of code, over 15K rows of data in some tabs, it's referencing hundreds and hundreds of pictures I've uploaded to a server, and processing various aspects of thousands of people I've inputted into this program. Did I overload this sheet somehow or is Google just over me right now (ie, does it not like me trying to use insertImage, for example, 100 times in one call..) Sorry, I've put so much effort into this and the "insertImage" function suddenly not working is a major blow to it when it is NOT the code that is malfunctioning. If it was the code at least I could fix it.

What's odd is I was running the program 2 days ago. Would look up, for example, 100 people and then have it show me all the pics on one page. Ran this a few times and in the middle one of the outputs it suddenly stopped working. I re-ran a query, asked it to show me pictures and it started placing like 20 of them and then just refused to show any more at all. This really seems like Google telling me to f8ck off.