Had a simple creative mode save that now fails to load with the newer version of this mod active. To recreate, load the following save, syncing mods with save. The hang does not occur if double speed belts mod is disabled.
https://www.dropbox.com/s/p7y734pbtjacr7q/0-creative%20tests-37%200.17.79-15.zip?dl=0

Update: Investigating further, the issue began with 0.3.0 and exists through all newer versions. Some change to support other mods appears to have broken it. Rolling back to 0.2.7 and the save loads without issue.

Update 2: Enabling Double Speed Belts 0.3.3 solo does not cause the hang, but then also enabling both Miniloader 1.8.5 and Ultimate Belts 0.17.1 causes the hang. With the other two mods still enabled, rolling Double Speed Belts back to 0.2.7 corrects the issue.

The version 0.3.3 has mod option to start in the same way as in 0.2.7.

I will test the reported issue in new year.

I changed the option you mentioned, and it did correct the issue, but I'm unsure what was causing the hang with the option at its default (checked).
I also noted that the mod option is listed as:
Unknown key: "mod-setting-name.dsb-autoprototypes"

I don't want to add new version for every new mod, so from version 0.3.0 all changing of prototypes come automatically. Sometimes with errors, but I need to know why and how they come.

Also note that with the option unchecked, the belt tier appears to be incorrect (starts with Yellow = 30). Rolling back to 0.2.7 with the other mods still present corrects the hang issue while also ensuring the correct base speed.

Tested, permanent loading of savefile without success.
It looks like a bug, that must be reported on the forum: https://forums.factorio.com/viewforum.php?f=7

Are there any additional items that I should report along with the bug report? Can you elaborate on the changes to the mod that might have resulted in the hang?

    {type = 'transport-belt', name = 'transport-belt', tier = 1},
    {type = 'transport-belt', name = 'fast-transport-belt', tier = 2},
    {type = 'transport-belt', name = 'express-transport-belt', tier = 3},
    {type = 'transport-belt', name = 'ultimate-belt', tier = 18},
    {type = 'transport-belt', name = 'ultra-fast-belt', tier = 6},
    {type = 'transport-belt', name = 'extreme-fast-belt', tier = 9},
    {type = 'transport-belt', name = 'ultra-express-belt', tier = 12},
    {type = 'transport-belt', name = 'extreme-express-belt', tier = 15},

Here tier is just the belt speed divided by yellow belt speed; so yellow one is 1; red is two times higher, blue (actually cyan) is three times faster than yellow. It was in vanilla. The
The same tier will be used for new speed calculations:
The yellow belt has the same speed as before, the red one (tier 2) is twice faster than yellow, the cyan (tier 3) is twice faster than red one.

Bug report: tier 6 or 9 or 12 or 15 or 18 are too high while speed = base_speed * 2^(tier-1).

Solutions:
exception for this mod, I need to use the table for this prototypes;
i need to check if here was wrong tiers: after tier 3 must be tier 4, not 6; it can be done on the side of Ultimate Belts
set the flag about incompatibility (conflict);
rewrite the tier system based on prototype.next_upgrade.

I've tried to get the maximum:

    if tier > 13 then tier = 13 end -- 14 was too high

So, highest speed if Factorio is about 4096 faster than yellow belt.

As you see, the Ultimate Belts mod has too high tiers and it must be somehow reduced.

May be it comes from

Shouldn't the use of Double Speed belts simply override those incompatible speeds, so that speeds then return to Yellow=15 -> Ultimate=1920? If I roll back to Double Speed Belts 0.2.7, all of these speeds work correctly, even when combined with the use of Ultimate Belts and Miniloader, so it appears that this was something that did work previously but broke with this mod starting 0.3.0. If the new speed calculation method is the issue here, is the new method really necessary? Can the mod option not simply revert back to the old (compatible) method without also incorrectly starting at Yellow=30?

You are right, the table in the data-final-fixes.lua must be corrected.

Fixed; All tiers are renumber to according the mod concept.

Understood and thanks for the effort. I have confirmed fixed with my config as well.

Question: Does the setting for this mod (Use automatically changed prototypes) still have a purpose with this new fixed update? Changing the setting no longer appears to have any impact.

It's not necessary, same as before, but it was helpful :)

In some situations the hand made table can be better than automatically generated table, but I cannot define this situations. Just keep it while it's not wrong.