Your dehum isn't big enough for the size of your canopy.
Fans move air around. They do not cool the air nor dehumidify it, or humidify for that matter. Fans can even various properties of the air out - like heat and moisture - but don't change those things.
59% is fine if the temps add up to a proper VPD for stage of life. However, if struggling to maintain and the plants are still growing, you will eventually run into high RH. If the plants are fully grown, all is fine and it won't get worse. The dehum has to keep up with rate of transpiration which is directly related to size of your canopy / size of plants.
If your ambient RH% is high, it also has to keep up with that. If your ambient RH% is higher than you need, then you also have to control RH of the entire room the tent resides. Closing it off might help. Exhausting outside might help.
For a 5x5 canopy and not living in a high RH% area (or your AC is on), i'd say a 50-pt/day (AHAM) dehum is a good choice and a 30pt might be enough -- not difference in pints per day at saturation or "AHAM." The rate at saturation is a nonsense number of no value. If you have high ambient rh, you may want a beefier dehum. You might find a 70pt/day AHAM but more likely have to get into "commercial" units and looking at 400-700 USD. commercial units are built better, too.
Better to go bigger than your need so it doesn't run so hard it dies in a few years.
manual says 10 L / day ... does not mention temp / RH for this measurement. It's only 200w. So 20pts/day at AHAM might be about right.. So, yeah.. a 50pt AHAM is probably enough as long as your outdoor RH isn't going to spike higher in a consistent way.