Black Beard Algae

There are a number of commercial products tailored for this.

Well,given that the Anubia are normally attached to wood ,possible organic matter from break down of wood(will alway's be taking place), and possibly fish food's or fish waste maybe getting lodged in/under the wood, then this may help feed the stuff.
One two punch and peroxide treatment are effective most times and if the stuff is coming back or is not being affected at all,then I might move the wood,vaccum under it,spray the root's with 3% peroxide and place em back in the tank.
Might also consider attaching the anubia to some rock rather than wood and see if this made a difference.
Just thinking out loud, while visually seeing my own 55 gal full of anubia and wood pieces that have been in the tank for nearly four year's.
I have bright green tuft algae over most of the wood but it suit's the plecos ,shrimp's,that inhabit the tank.
I kinda like it, but realize that not everyone does.

Upping the CO2 to 40+ppm, clean the canister and spraying Excel, 1ml per 10L, directly onto the BBA works for me.

Remove and clean as much as you can manually (outside of aquarium because you can spread it whyle removing). Power off filter and when water settles take a syringe and apply 3% hydrogen on affected spots you are unable to remove manually. Leave for 30minutes before powering on filter. Shrimps and snails are heavily affected if in contact with hydrogen.

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