xp storage robs me of xp and in survival it is a headache when I save my xp and it takes it away from me
MINECRAFT JAVA FABRIC 1.21.5

Levels are not linear in Minecraft. What you want to look for is the actual total XP value in the brackets, which adds up just fine in your video as you can see (500+500=1000). If you go from level 0 to level 19, you need 500 XP points. But due to higher levels needing more XP points, adding 500 points to 19 levels will not give you another 19 levels.

For further explanations, see https://minecraft.wiki/w/Experience#Leveling_up