Update problems

Hey there, I've been experiencing an issue for the past few months and I'm just wondering if anyone can help me.

My updates have always worked 100% fine, until I upgraded to Catalina. I am stuck on 15.0.

I have an available update for 15.4. I have followed the procedures of downloading, restarting. Where there would normally be a boot partition for the update, there is nothing, and it boots me back into 15.0, with a pending update.

I have researched this for days, I have tried updating Clover, all my kexts, enabling/disabling SIP, safe booting etc.

Nothing I have tried has worked. If any of you could assist me I'd be incredibly grateful!

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Gigabyte B250M-DS3H

Intel i7-7700K

16GB RAM

Asus RX 580