Troubleshooting more than one component at a time, in your case three mics, can be a mental and technical challenge. As soon as a second or third item is used as comparator, the assumption is usually: "This one is healthy, so the other one must be defective!"
First, an AT4033 should not be quieter than the two Neumann models you mention, especially not when compared with a super-quiet model like the TLM103.
So, it is possible, but would be a rare circumstance, that all three microphones are defective, or that, equally likely, something has gone haywire in your signal path downstream from the mics.
Here is what I would do: establish a baseline: borrow a well-working U87. Position U87 (proven as good) and U87 (possibly defective) next to each other. Singing a steady tone, set gain to similar levels at the board. Now, with no input into the mics, crank the monitor level of the board to compare noise floor of both mics.
This will be the first objective and useful troubleshooting test of several to follow.
Let's say, the U87 (possibly defective) has indeed a 6dB or higher noise level than U87 (good). That still could indicate a healthy U87, if it's one of those U.S.-delivery U87s (some came with as much as 12dB lower gain!) You would need to consult your schematic and check whether pads and 50 Ohm strapping are in place in your mic, and bridged pads and 200 Ohm strapping are found in the "good" mic.
The U87 issue is completely different from the TLM 103 issue which shares NONE of the components and circuitry of the U87, old or new style. Here, again, I suggest comparing noise floors with another TLM103 by borrowing, or buying one on try-out. If your mic turns out defective, only Neumann/Sennheiser have the parts and circuit information for repair.
Best of luck,
KH