If you make a character with 8 levels in arcane trickster, and 7 levels in eldritch knight, the character sheet will only display 2nd level spell slots for them, not 3rd level, despite having 15 levels in quarter caster classes (15/3= a caster level of 5, but the sheet is likely calculating the classes separately for 2 caster levels each, and setting them to caster level 4)

Likewise, a character with 5 levels in ranger and 5 levels in paladin is not being given their 3rd level spell slot.

Also, homebrew pact magic features still dont display spell slots correctly unless you add a level of warlock to the character

According to Crawford’s tweets you divide and round down each class separately then add the levels together 'https://www.sageadvice.eu/paladin-3ranger-5-caster-level-⌊3252⌋4-or-⌊32⌋⌊52⌋3/

PHB:

Spell Slots. You determine your available spell slots by adding together all your levels in the bard, cleric, druid, sorcerer, and wizard classes, half your levels (rounded down) in the paladin and ranger classes, and a third of your fighter or rogue levels (rounded down) if you have the Eldritch Knight or the Arcane Trickster feature. Use this total to determine your spell slots by consulting the Multiclass Spellcaster table.

You work out each classes contribution first and then add them all up. So you divide Arcane Trickster levels by 3 and add them to the pool. Then you divide Eldritch Knight levels by 3 and then add them to the pool. You don't divide afterwards - because each class can have a different divisor.