A game can run at a high frame rate and still hitch briefly when something new appears on screen. On PC this is frequently shader compilation rather than a performance shortfall.
Consoles compile once, PCs cannot
A console has one hardware configuration, so the developer can translate every shader into final machine code before the game ships and include the result on the disc.
A PC game faces an open set of graphics processors, driver versions and settings combinations. The final translation cannot be done in advance because the target is unknown until installation.
The work therefore happens on the player's machine, and the only question is whether it happens before play begins or in the middle of it.
Compiling during play blocks a frame
When a new visual effect appears for the first time, the driver must compile the corresponding shader before that frame can be drawn.
Compilation takes long enough to miss the frame deadline, which the player sees as a sharp hitch precisely when something interesting happens on screen.
The hitch is usually one-off per effect, since the result is cached, which is why a level that stuttered on first entry runs smoothly afterwards.
Pre-compilation moves the cost
Many games now compile shaders during a loading screen or a one-time step after installation. This does not reduce the total work, it relocates it to a moment the player expects to wait.
The step can take several minutes and must be repeated after a driver update, because the compiled output is tied to the driver version that produced it.
Players sometimes read this as a defect. It is the visible form of work that would otherwise be spread invisibly through the first hours of play.
Caches are fragile by design
Compiled shader caches are invalidated by graphics driver updates, hardware changes and game patches, because none of the previous assumptions are guaranteed to hold.
That is why stuttering can return after an update on a game that had been running cleanly for weeks.
Some engines ship pre-generated caches for common hardware, which reduces the work but cannot eliminate it across the full range of configurations in use.
Engine design affects severity
Engines that assemble shaders from many small combinable pieces generate a very large number of variants, and each variant is a separate compilation.
Engines that use a smaller fixed set produce fewer variants and therefore less first-run work, at the cost of some flexibility in how effects are authored.
This is why the problem is far worse in some titles than others despite similar visual complexity, and why it tends to cluster around particular engine families.