Almost a year ago I bought a Dracaena fragrans plant of 2 meter in height which has since lost a lot of its leaves. The plant often loses leaves in a certain process. Every time a leaf is going to turn brown, it develops one or more yellow or brown marks in the middle of the leaf which are eventually connected until the leave has completely turned brown.
These are photos of three different leaves in different stages of this process. Additionally, many leaves at the bottom side of the plant look limp. As you can also see in the picture, one branch completely or partially turned dark brown. About 3 out of 10-15 branches turned brown like that one.
My apartment views the west, so in the summer on sunny days, the plant receives direct sunlight in the evening for a couple of hours at most. Recently I experimented by putting the plant outside in full sunlight, but that only burnt the plant so at the end of that day I had to remove about 15 leaves which had been scorched. Apparently lack of sunlight is not the problem.
Location: the Netherlands.
The plant does not look very healthy and I estimate that it has lost half of its leaves in the past year. What could be a typical cause of these brown and limp leaves?