Blueprint wipes
The most misunderstood part of a Rust wipe. A map wipe and a blueprint wipe are different events, and only one of them happens every month.
What a blueprint wipe clears
Blueprints are the crafting knowledge you unlock through the tech tree or by researching items you find. They persist across map wipes, which is why by the second week of a cycle most of the server can already craft rifles.
A blueprint wipe resets that knowledge to nothing. Everyone is back to stone tools and has to research their way up again, on top of losing the map.
Why it changes the whole first week
On a map only wipe, the race is for position: land claim, base spot, monument control. Guns arrive fast because everyone already knows how to make them.
On a blueprint wipe, the race is for knowledge. Scrap becomes the most valuable thing on the server, the tech tree decides who is armed first, and the early game runs much longer. Raiding starts later because nobody can afford it yet, and small teams do noticeably better because a large group cannot convert numbers into rifles as quickly.
How often they happen
Blueprint wipes are not on a fixed monthly cadence, which is exactly why the question keeps coming up. They are announced rather than assumed, and the sensible way to find out is the announcement for that month's update rather than a rule of thumb.
When a blueprint wipe applies to a Scarab server, it is stated on that server's page and in the wipe announcement before it happens, never discovered by logging in and finding your tech tree empty.
The short version
Map wipe: you lose your base and your stuff, you keep what you know. Blueprint wipe: you lose what you know as well. The first is monthly and certain, the second is occasional and announced.