This morning I removed the leaf of the picture from my jade plant. What you can see is the back side. There is another leaf with the same type of damage. During the last month my oldest jade plant seems to be growing slower than usual and it has lots of leaves that do not look very well.

I repoted it about three weeks ago. Since a year ago it has been in a gritty mix, and that is still the case. When I repoted it, I didn't find any evidence of rot, bugs, insects or anything else suspicious, so I wonder whether it suffers from something too small to be seen or something else like lack of nutrients or the London spring weather?

This month I've started to fertilise it again with a cacti fertiliser, shown in the second picture. The damage started before I began fertilising so the two things can't be linked.

Perhaps this type of damage is normal and I'm just worrying unnecessarily?

Just in case I'm keeping this plant away from my other jades and portulacarias.

Many thanks for your help in advance.