RP2040 Board receiving weird output from SparkFun Ublox NEO-M9N GPS Unit
Just in case you wonder how to do this &quot;by the book&quot;. Assuming these vias are plated on both sides and connected, then the proper way to solder them (as per IPC standards) would be:

Peel &amp; cut the wires so that no more than 0.5mm protrudes on the solder side. About as far as an insulated AWG24 wire is thick, so you could use such a wire as template.
Measure and cut before soldering.
Ideally, fixate the wire to the board using tape or similar before soldering, rather than bending it on the solder side just to hold it in place.
The solder should wet on both sides, forming a cone shape around the wire on both sides. You shouldn't be able to see the via on either side, it should be completely covered. You might be using too little solder or you remove the solder iron too early, leaving a &quot;cold joint&quot;. The blob on &quot;A3&quot; on one of the boards would be an example of such a cold joint.

For general experiment board stuff, I'd also recommend to use multiple strand wires since these are less prone to silently break.