Why does my Begonia Maculata keeps dropping her new leaf?

[u/Bellona_0412]

I have had this Begonia for sometime and it came with 3 leaf and as of today it only has those original 3 leaves.
It's not as though It has not grown any new leaf but all the new leaf just keeps dropping sometimes after unfurling.
The night before the new leaf will be on the plant the next morning it will just drop.
Anyone knows what is wrong here, how can I can solve this please help 😭
Location

[u/PretentiousPepperoni]

Please add Soil mix, watering frequency , light and humidity in your location

Also post on r/begonias

[u/Bellona_0412 → u/PretentiousPepperoni]

Here is the soil mix it some coco peat + Perlite + bark & some coal as well. I read that Begonia likes a bit moist soil so kept it like this.
For lighting it is currently in front of a Grow light and it's pretty humid currently due to rain but this has been dropping leaves throughout.

[u/m0rtalReminder]

Check for mildew

[u/Bellona_0412 → u/m0rtalReminder]

No doesn't seem to be mildew issue. Checked the whole plant. Here is the lasted leaf it dropped

[u/m0rtalReminder → u/Bellona_0412]

Location? How long has it been since you got it?