20th level multiclassed character (both classes as well as as race are custom) 4th level spells not showing. 1st 2nd 3rd and 5th show with no issue. Manage spell inventory shows selected spells but does not register on main menu spell selection for that level at all. 

Post the url to the character sheet so someone can take a look.

Is one of those subclasses a Warlock by chance?

yes it is

Reread the Pact Magic section of the Warlock class. Pact Magic doesn’t work the same as Spellcasting.

I apologize I am not following. I should have spell slots for 4th level, no? The spells have been selected and learned....

No. Again, reread the Pact Magic rules.

Pact Magic

Your arcane research and the magic bestowed on you by your patron have given you facility with spells. See Spells Rules for the general rules of spellcasting and the Spells Listing for the warlock spell list.

Cantrips

You know two cantrips of your choice from the warlock spell list. You learn additional warlock cantrips of your choice at higher levels, as shown in the Cantrips Known column of the Warlock table.

Spell Slots

The Warlock table shows how many spell slots you have to cast your warlock spells of 1st through 5th level. The table also shows what the level of those slots is; all of your spell slots are the same level. To cast one of your warlock spells of 1st level or higher, you must expend a spell slot. You regain all expended Pact Magic spell slots when you finish a short or long rest.

For example, when you are 5th level, you have two 3rd-level spell slots. To cast the 1st-level spell witch bolt, you must spend one of those slots, and you cast it as a 3rd-level spell.

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.

Additionally, when you gain a level in this class, you can choose one of the warlock spells you know and replace it with another spell from the warlock spell list, which also must be of a level for which you have spell slots.

Quote from LEIFWAGNER >>

20th level multiclassed character (both classes as well as as race are custom) 4th level spells not showing. 1st 2nd 3rd and 5th show with no issue. Manage spell inventory shows selected spells but does not register on main menu spell selection for that level at all. 

 whats the levels of your multiclass?

ranger 11 warlock 9

Level 9 warlock has 2 5th level pact slots. 11th level Ranger has 4 level 1, 3 level 2, and 3 level 3 spell slots. Your build does not allow you to have a 4th level pact or spell slot.

Again, reread how Pact Magic works.

Thank you