From the page at https://support.patreon.com/hc/en-us/articles/360026984152-I-m-locked-out-of-posts-I-should-see:
Important: If you see “Custom pledge” it means that you’re not currently in a tier.
Meaning, if I pledge $10 for someone that has the closest tiers at $5 and $25, I won’t get the reward from the $5 tier. So if I want to get that reward, I either have to pay $25 or $5 now.
I absolutely think that it would make much more sense to give all benefits of the tiers that require the same or lower amount than the custom pledge.