The total sum of your weapon/armor value cannot exceed your current character level inside of PotD.
This means that if your weapon/armor value is 30, then you will not receive a bonus from silver chests until you reach level 31 within PotD.
That sounds good right? So long as you reach the right level, then you will get bonuses from silver chests.
There is still a failure rate even when your PotD character level exceeds your weapon/armor value. As best as I can tell, this failure rate increases as the gap between the two values decreases. So if your weapon/armor value is 30, and you open a silver chest at level 31, your odds of getting a bonus are very, very low.
With this in mind, the best way to start getting bonuses on your weapon, after you inevitably have to reset your progress data, is to full clear every floor of PotD. You get all the joy of killing very trivial monsters with the full knowledge that any silver chests you come across are useless to you.
Let’s say you’re at 29/30 on your PotD weapon/armor value. Every silver chest you find prior to hitting level 60 is guaranteed to not give you a bonus. Upon hitting level 60, the gap between your character level and your weapon/armor value is very small, and so the failure rate on the upgrade is very high.
So if you’re nearing the end of your PotD weapon run, you’ll end up running through ~45 floors where a bonus to your weapon/armor is impossible. Upon reaching a point where you can receive a bonus, you’ll be fighting against the RNG of a silver chest showing up on a late 40s dungeon floor, and then against the RNG of the failure rate on that silver chest. Effectively, for the chance at a few floors worth of opportunity to receive a bonus at the end of the content, you must always replay the content from the beginning at floor 1. Don’t think about racing through the floors as quickly as possible either; if you don’t have a character level higher than your weapon/armor value, you will not get a bonus from silver chests. All of this instead of being able to replay the last 40-50 set of floors, where you would be just battling RNG.
If you’re reading this and thinking to yourself “my gosh, that sounds terrible”, then I have good news for you. That reaction means that you’re not insane.