I wonder if the bumps are intumescences. I can't find a picture of them on Thunbergia to see how they compare with Christoph's image but this is what intumescences look like on Cuphea:
https://negreenhouseupdate.inf...
and here on Cleome:
https://negreenhouseupdate.inf...
If that's what they are and the cause is believed to be reduced UVB radiation, then perhaps the plant is getting insufficient light. It looks from the pictures as though it may be growing indoors?
