Minor issue but when you multi class the Blood Hunter subclass Profane Soul with Warlock, the spell selection does not take into account that the Warlock spell selection is supposed to be the Warlock level + 1/3 of the Blood Hunter levels. Thanks! 

There is some confusing wording on the profane soul multiclass rules. The PHB multiclass rules say every class chooses their spells known as if they were not multiclassed.

If I had to guess, I think the wording is such because as of now on DnDBeyond, I appear to have 2 sets of spells, one for BH and one for Warlock. It also shows up as my character having 2 separate spell slots for each. Don’t get me wrong, I’d love to have 4 spell slots as a warlock, but that wouldn’t make a lot of sense as I’m getting the magic from the same patron. With the 1/3 of BH levels added to the Warlock levels, you have more spells known, higher levels, but you retain only a total of two spell slots. 

I'm not entirely sure what you are talking about. I just made a test multiclass and it doesn't give 4 spell slots. Compared to the blood hunter multiclass rules, the only thing DDB does incorrectly is allows too many cantrips:

If multiclassing Order of the Profane Soul with Warlock levels, add a third of your blood hunter levels (rounded down) to your Warlock level and consult the Warlock progression table in the Player’s Handbook for total Spell Slots, Cantrips known, and Spell Slot Level.

Okay, I think it’s a mix of me misunderstanding, and it’s been fixed. Last night, I had a total of 4 spell slots, and that’s been fixed.  The other half was a misunderstanding on my part. The multiclassing entry says that 1/3 of BH levels means “total Spell Slots, Cantrips known, and Spell Slot Level.” I do have a 3rd level spell slot, but that doesn’t include SPELLS KNOWN. So I have the 3rd level spell slot, but I don’t know any 3rd level spells. Thanks for helping me think this through. 

I'm still experiencing issues with this, I'm dipping into warlock on my BH & adding levels of either class is not affecting the other's slot level. My 12 BH/2 Warlock should have level 3 spells available for both classes but the BH is still level 2 spells max and the warlock is level 1 spells, they don't seem to affect each other.

Quote from Terrisare >>

I'm still experiencing issues with this, I'm dipping into warlock on my BH & adding levels of either class is not affecting the other's slot level. My 12 BH/2 Warlock should have level 3 spells available for both classes but the BH is still level 2 spells max and the warlock is level 1 spells, they don't seem to affect each other.

 You shouldn't be able to learn level 2 spells with BH and level 1 spells with Warlock, then have level 3 slots to cast them with.

I'm referring to the optional Profane Soul multiclassing rules:

Multiclassing with Warlock. If your blood hunter is part of the Order of the Profane Soul and also has warlock levels, add one-third of your blood hunter levels (rounded down) to your warlock level and consult the warlock progression table in the Player’s Handbook for total spell slots, cantrips known, and spell slot level. You should consider aligning your Otherworldly Patron feature between both classes, but your DM might allow you to have two different patrons at their discretion.

So with that my unified casting level is 12/3 = 4 BH + 2 warlock = level 6 warlock. Warlocks get access to level 3 spells at level 5, so in this scenario I should be able to access level 3 spells for either BH or Warlock spells known.

Quote from Terrisare >>

I'm referring to the optional Profane Soul multiclassing rules:

Multiclassing with Warlock. If your blood hunter is part of the Order of the Profane Soul and also has warlock levels, add one-third of your blood hunter levels (rounded down) to your warlock level and consult the warlock progression table in the Player’s Handbook for total spell slots, cantrips known, and spell slot level. You should consider aligning your Otherworldly Patron feature between both classes, but your DM might allow you to have two different patrons at their discretion.

So with that my unified casting level is 12/3 = 4 BH + 2 warlock = level 6 warlock. Warlocks get access to level 3 spells at level 5, so in this scenario I should be able to access level 3 spells for either BH or Warlock spells known.

 So was I. Spells known are not "total spell slots, cantrips known, and spell slot level" that the multiclass rule specifically mentions, so it doesn't change spells known.

I see that the slot level is indeed leveled up, the slot level should = the level of spells you can learn. If my unified slot level is 3 then I should be able to learn 3rd level spells, not just cast upleveled 2nd level ones. 'Spells known' is the number of spells you know, the slot level is what dictates the level of spell you can know.

From the Warlock rules:

Spells Known of 1st Level and Higher

At 1st level, you know two 1st-level spells of your choice from the warlock spell list.

The Spells Known column of the Warlock table shows when you learn more warlock spells of your choice of 1st level and higher. A spell you choose must be of a level no higher than what’s shown in the table’s Slot Level column for your level. When you reach 6th level, for example, you learn a new warlock spell, which can be 1st, 2nd, or 3rd level.

Spell slots go by multiclass total levels. Spells known you by individual class levels. If you hadn’t multiclassed and only had the Warlock levels then you would only have 2nd-level slots and so therefore could only learn 2nd-level spells. So that’s the highest level spell you can learn, even though you have 3rd-level slots. That’s just how the rules for multiclassing spellcasters works.