As far as I can tell the remastered summoner states “You add to this spell repertoire as you increase in level. Each time you get a spell slot (see the Summoner Spells per Day table), you add a spell to your spell repertoire of the same rank. At 2nd level, you select another 1st-rank spell. At 3rd level, you add the first 2nd-rank spell to your repertoire. At 4th level, you gain your second 2nd-rank spell, and so on. When you add spells, you might select a higher-rank version of a spell you already have so that you can cast a heightened version of that spell.”
Meaning at level 18 you should know 2 spells for every level. However the character editor only lets you learn one spell of level 3-8. Almost halving the amount of spells in the repretoire.