I've seen it enough. Case in point, back in the 80's a friend of mine worked at Microsoft. A manager came to him with a lament that there was a program that compiled to 50K, written entirely in macro assembler. It had a bug in it. He had assigned it to multiple programmers, each of whom failed after trying to fix it for several weeks.
The problem was the author had invented his own language with the macros, left it completely undocumented, and nobody was able to make heads or tails of it.
My friend said, no problem, he'd give it a try. 2 hours later he had fixed it and checked it in.
Astonished, the manager asked him how he'd figured it out. My friend said he didn't. He ran it through the disassembler I'd written https://www.digitalmars.com/ctg/obj2asm.html (which is why he related the story to me) because it turned object code into asm source code. Found the bug, fixed it, and checked in the new source code.
Not only that, I discovered I could not read my own macros a few years after I'd written the code.
I've seen similar terrible examples that make use of expression templates in C++. They were all the rage for a couple of years. Fortunately for C++ programmers, expression templates are so miserably slow to compile that a blessed damper was put on the exploitation of this discovery.
Feel free to disagree with my assessment of this. You'll have plenty of company. But use macros enough and eventually you'll agree with me :-)