Updates to this task:

Ah, then is the missing file I detected yesterday. @Brecht Van Lommel (brecht) did a hack to compile, but with a empty file.

We can consider this as a non supported python api, so we can close the bug.

This is the reason of T56283 and T56284.

I can confirm in windows

This is also related to T56294

T56283 is related to this because the problem is the object link data.

@Campbell Barton (campbellbarton) I have a windows compiler error because you added "gizmo_types/blank3d_gizmo.c" to make file, but the file is missing.

Looking in detail in python API, the add function will never work because when adding a weight to vertex in a mesh, the vertex 1, 2, x is know, but in grease pencil, the vertex 1, 2, n is not like that, first you need define in what layer, in what frame and in what stroke are you adding the weight.

Steal the task

@goat head (goathead) You could use a different approach.

I can confirm this, but it's not a bug but an unsupported python API feature.

Good idea!

@Joshua Leung (aligorith) I fixed this in the past, but you removed the code, so I don't know how fix it now because I don't know enough how transform center works.

I have used your patch and had to make some more changes because when apply opacity the result was not equal. The problem affected all modifiers (Tint, Hue and Opacity).

I will take a look.

we need ask to @Daniel Lara (Pepeland) (pepeland) . Daniel, the test you did in surface did break anything in wacom or other windows computers?

Don't worry I have found the solution

@Brecht Van Lommel (brecht) Using give_current_material() fix the bug, but I have a new problem now, using BKE_object_material_slot_find_index(ob, ma) always returns 0, but when the material is at data level returns the right index. What I'm doing wrong?

@Brecht Van Lommel (brecht) Thanks for the info, I going to try to fix it. And agree, why have an exception here?

The strength is updated because deformstroke use a pointer to stroke, so the point is affected.

@Luciano Muñoz Sessarego (looch) I have fixed the problem but your file still has a problem with the user count of the image. This is not related to grease pencil and it looks the result of any previous crash. Maybe you could remove the image and save/reload, but not sure.

The problem is with Instance modifier, not sure why.

Still some problems.

I think I know where is the problem. I will fix tomorrow morning.

This was replaced by T56266

Thanks @Charlie Jolly (charlie) for catch the bug. I want to redesign the modifier apply.

Ok, as this is more a feature request because today this is not supported by design. I'm going to fix the crash setting a limitation to sculpt while play animation.

Not sure if this is something we need limit. What is the point to sculpt or edit while you play animation?

@Colby Klein (shakesoda) I don't know enought the event code to answer your question about commit your change or not. Could you ask to Campbell or Sergey (they know how works this area)

Replaced by commit ccf794dfc4c8

@Charlie Jolly (charlie) I have fixed after doing some more cleanup ccf794dfc4c8

sorry, I have read wrong the diff file... testing

Could you take a look? I'm unable to find the reason of the bug (see the mail I sent you about this issue)