So I created a new pair of diamond boots so they had no prior work on them and was applying my enchantments on them in the cheapest order of cheapest enchantments first such as mending when it became too expensive too apply thorns III and soul speed III which were last since those required more more xp than the others. I Have done this before with two other pairs of boots so I know it can be done. This was later confirmed in creative with books only holding relevant enchantments with the same results, TOO EXPENSIVE right before thorns III and soul speed III. In short I could do it before, why can't I do it now.

Steps to reproduce
Attempt to add these enchantments in order listed:
Mending - 2xp
Unbreaking III at 4xp
featherfalling IV at 7xp
Fire Protection at 11xp (Note: Featherfalling and fire protection have same cost thus order of either does not matter)
Depth Strider III at 21xp
neither soul speed III or Thorns III can't be applied due to being "too Expensive"
The diamond boots were new with no earlier work done on them. Normally you can put the two last enchantments on and rename the boots as shown in the other video without issue. Rather it becomes too expensive even though the previous cost was only 21xp which only a little over half of the 40xp limit.

See attachments below