I've narrowed the bug down to the following set of mods:

A Sea Block Config
Angel's Petro Chemical Processing
Angel's Refining
Angel's Smelting
Base mod
Bob's Electronics mod
Bob's Functions Library mod
Bob's Logistics mod
Bob's Metals, Chemicals and Intermediates mod
Bob's Ores mod
ScienceCost Tweaker MOd (mexmer)
Sea Block
Space Extension Mod

Adding either of the following mods works, but combining them results in an error when starting Factorio:
Bob's Technology mod or bobstech
Angel's Bio Processing

Producing the following error message:
Screenshot of this error message: https://imgur.com/0DDGTKY

Failed to load mods: Difficulty normal: Cycle in technology tree detected.

ore-crushing
-> basic-chemistry
-> angels-sulfur-processing-1
-> slag-processing-1
-> steam-power

electricity
-> ore-crushing

Disabled all mods, Restart, Exit

Please fix this.

I would recommend turning off "Burner phase" in bobtech, you may need to disable Angel's mod first to make the game load and be able to access the setting. You have to do it from the main menu (Or download a tool to edit settings outside of the game.)

It's disabled by default because of the incompatibilities with other mods.

Thanks for the help, that does solve the problem.
With Sea Block you don't really need the burner phase anyway because there's no coal at the start.

I've updated Sea Block to disable and hide the burner phase setting.

Still having this issue. when burner phase is disabled

Still having this issue. when burner phase is disabled

Can you be more specific?
what kind of issues? is there an error message?

Having a similar issue.

Failed to load mods: Difficulty normal: Cycle in technology tree detected.

steel-processing
-> basic-chemistry-2
-> water-treatment-2
-> slag-processing-1
-> steel-processing

Seems like I need to have all 3 of the below mods active for the error to come up?
Angel's Petro Chemical Processing
Bob's Electronics mod
Sea Block

Otherwise, all I'm doing is trying to activate Seablock and all its dependencies

Having a similar issue.

Failed to load mods: Difficulty normal: Cycle in technology tree detected.

steel-processing
-> basic-chemistry-2
-> water-treatment-2
-> slag-processing-1
-> steel-processing

Seems like I need to have all 3 of the below mods active for the error to come up?
Angel's Petro Chemical Processing
Bob's Electronics mod
Sea Block

Otherwise, all I'm doing is trying to activate Seablock and all its dependencies

Sea Block isn't yet compatible with the latest versions of Angel's mods. Roll them back and everything will work fine! Required versions of all the mods are listed on the Sea Block forum post 🙂
https://forums.factorio.com/viewtopic.php?t=93136

I expected Sea Block compatibility as a new version was released last month.
In order to downgrade these mods I downloaded the older versions (where an older version was listed) and I also had to get rid of the newer versions (move to backup).