During my first months with my first RPi3B kit, I bought a breadboard kit similar to this
https://www.amazon.com/Paxcoo-Breadboar ... readboards
there were loose connections, and on other points, very tight holes making it hard to insert even 1/4W resistor leads.
then I bought ones from the local electronics shop. though a little bit more expensive, all insertion points/connections were ok.
when I disassembled the problematic breadboards, it seems that the metal contacts are stuck to the plastic casings, some were deformed, thus the loose and/or very tight fit.
I was able to repair most of those, and use the breadboards for LED-resistor array (for my LM3916 VU meter) and not use it for ICs and other active components
Nowadays I often use the breadboards bought from the local electronics shop....