I am sure that the combination of rain and then humidity won't help things. One of the plants - the one with leaves edged in brown and yellow discoloration - is now showing many more leaves, some new, like this. So there is definitely something wrong there with that one. I cut off any leaves on other plants that are yellowing or show signs of emergent blight. I'll have to poke around a little deeper in the leaves and see if I can spot any insect eggs that might be hiding.

you have, from the pics, an 'ornamental' (fruitless) cherry tree named 'wine' or 'burgundy' something after the leaves. all cherry, plum, peach trees weep a certain amount of sap, much like pine trees. they leave from wounds in the bark that can be caused by pruning, abrasion, insect infestation, or natural 'growth' breaks in the bark the clean, dried sap is a non unpleasant 'resin' type incense. I would scrape some of that away, and see if you have insects chewing up the tree bark (you'll see holes going into the branch) - that's one of the prime causes around here.

repotted very very rarely. But it's always done very well. potting medium is regular potting soil. But the plant has never had any problems before.

I had one of these plants some years ago. I had it outdoors for the summer and brought it in before winter. The leaves started to yellow and drop off. I started seeing tiny flying insects dead on the floor near plant. On examining the soil I found tiny white insect eggs. I almost lost all my inside plants. I used dish soap and water spray to all my plants along with removing each plant from dirt and dipping the roots in dish soap water making sure allmost all dirt is off roots.l washed the flower pots of all dirt and repotted all in fresh potting soil spraying all the plants thoroughly again 5-7 days later.