Hey crnopivo,
Sorry for any confusion here! We can see the before/after currency status for recent transactions like this, though that sounds like it may have been missed.
In this case, the most recent change before those purchases was from receiving 30 crafting materials in a pack the day before these skins were purchased. That increased your total crafting materials to 5215, with the subsequent purchases and crafting material gains all seeming to match up.
It looks like crafting materials were also gained just under a month ago which shows a similar amount, so from what I'm seeing here there doesn't appear to be anything missing, fortunately.
If something else was crafted to bring you down from ~20k to ~5k crafting materials, that would have been over a month ago if that timeframe helps recall anything else. Otherwise, is it possible there's another currency you may have been seeing instead, such as Legend Tokens? Hope that helps clarify a bit!