Too much water (4L every two days)?
Too much air moisture?
Too much temperature range between day and night?
Maybe… a fungal desease? 
Don’t know but I do know raspberry suffer root rot easy make sure you have well draining potting soil and the roots aren’t constantly wet
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I agree make sure soils not too wet…just like most other plants let soil statt to dry out between waterings…4L every 2 days seems like allot of water to me unless its like 100f all day
How dry does the soil gets? My vote goes for lack of water, unless you are using clay for potting soil.
You see how some of the older leaves have brown edges? That’s a sign of lack of water. When water is lacking the tip of the leaves are the ones that get short changed.
Saturate the pot, wait an hour, weight. Weight again 24 hours later, see how much water is evaporating. aim to replace that.
Sounds like too much raspberry watering for potted plants, even large-ish pots. Once the roots are affected, symptoms can appear similar to lack of water.
If wilting persists at a certain point in the cane, look closely for evidence of borers or girdlers.