That is why you encountered that issue.
Mixing RAM running in dual channel mode is not recommended
Even if you use similar models, is not recommended to mix different RAM modules.
To avoid issues, modules with identical specifications found on a RAM kit should be used when running in multi-channel mode.
It is hard to predict the outcome when you mix and match modules that were not tested to work together. A motherboard could even refuse to work all together.
The RAM that goes into a RAM kit (package) has been tested to work together. There are times that different RAM modules, even if they look similar, and have the same model they could have different IC chips brands.
Manufacturers don’t guarantee mixing or adding one RAM modules to another, even when they are the "exact same" model.
There are many memory companies (e.g. Kingston/HyperX) and only three DRAM chips manufacturers (Micron, Samsung, and Hynix) .
A memory company like Kingston/HyperX might sell the same RAM module with chips from different DRAM chips manufacturers or internal timings that differ.
Sometimes they might play nicely with one another and some other times they just refuse to work.