Hi Melissa, welcome to the forums.
While this is not a botany forum per se, you will probably get some decent ideas. Most of us are growing things in a permaculture/polyculture fashion, so a plant in a pot is not a common growth style on here. Honestly the picture of the pot is more diagnostic than the leaf to me.
First thing is that plants get transplant shock. They may have some terminal die-off and many will lose entire branches. This correlates to
root health, if a root on a given side is compromised the upper plant on that side will often manifest.
Bryant RedHawk is the resident mad scientist on transplant shock and if you search for multivitamin you will see how many times he has recommended use of expired multivitamins for this purpose.
Second is that the drainage in this growth system is poor. Even if you have some holes drilled in the
bucket it is very hard to keep the moisture proper throughout, and you will get fungal issues which can look like this, especially in damp warm climes. It would help to know your zone/climate.
Third is that nutrient imbalance can cause this kind of distal leaf damage. You have done well to top dress with manure, but the other minerals are just as important, and nitrogen excess in relation to other things can be destructive.
Fourth is you will find, especially on here, stories of manure and hay/straw tainted with herbicide. These can be remarkably persistent, and cause vague malaise and die-back in plants.
#1 will take care of itself with tincture of time, 2 will be best corrected by growing in real soil (raspberries can be grown in containers but probably would be better served in a buried pot with the bottom mostly gone to limit spread if that is your desire), 3 would be only diagnosed with an expensive soil test for one pot(!) or you could just wing it and add rock dust and likely have about what you need, and 4 sucks to be you, that soil is toast and needs to spend time with mycelium to degrade the herbicide.
There are other possible causes, like phytopthera which is my nightmare, but those are the low hanging fruit in my opinion.