I remember you posting that you recently did some repots. Not every tree overcomes that damage in a few weeks. And even if they do, the effects on the foliage don't disappear if the foliage isn't replaced; once it's damaged, it'll stay damaged.
Open wounds can get infected no matter the climate or conditions.
It's not just fungi, but also bacteria and other micro organisms, and insect larvae.
The signs are all the same on the top of the tree, but on the bottom there are different things going on that we can't see. But we can smell it sometimes, with some deduction most issues can be traced back or related to certain events or conditions.
Usually a lack of oxygen is a jumpstart for all of the above; some root parts die, this attract insects, the insects poop harmful bacteria, yeasts and fungi from their gut microbiome, the cycle continues long after the lack of oxygen is resolved.
Fungi and bacteria can linger as long as the tissue bleeds and supplies them with nutrients and water.
For a good diagnosis, we have to take all those elements into account, and logically go forward combating or acknowledging all of those elements.
There are very few people in the bonsai world with enough knowledge about plants and gardening to fully understand how plant disease develops and progresses, or where the cause and effect can blend into each other. This is no accident or lazyness on their side, because it's not just knowledge of plants and substrate, but almost all biologically influential factors; viruses, bacteria, fungi, other micro organisms, insects, physics, (bio)chemistry, physiology and so on. I've been studying and working for 15 years on those things and I still learn new stuff every day and people correct me more than weekly.
Most issues can be resolved by adjusting your behavior and habits, and giving the tree time. That's enough for most people to know, really. You can do bonsai without issues for decades with just that practice of 'whoops, adapt, wait, overcome'.
A little peroxide fixes a lot of issues as well.