People who see this as a sort of civil war prelude or a sign of crisis for Zelensky should probably hold their horses. The conflict between SBU and GUR is deep and has a long history and mostly it's about dirty business and money.

The SBU has officially accused that RDK guy whom they blackbagged of offering hitman services (to Russia, of course). It's an open secret that Ukrainian military intelligence offers contract killings (for example, that bombing in Monaco in June) as a side gig. So maybe the SBU doesn't like the competition, or the optics, or maybe GUR just didn't kick up enough.

Maybe the contract killing stuff is a pretext and it's about drug money or arms trafficking. Or scam call centers. The various Ukrainian intelligence agencies all dabble in this stuff or make money from it.

In any case, it's mostly just a turf war between gangs, not inherently "political" (even though the various factions have different political backers, e.g. GUR is Budanov's domain, and he is now Head of the Presidential Office, not just a military guy).