Replaying the trace on radeonsi generates lots of GL API errors:

Mesa: User error: GL_INVALID_FRAMEBUFFER_OPERATION in glClear(incomplete
framebuffer)
Mesa: User error: GL_INVALID_FRAMEBUFFER_OPERATION in glDrawArrays(incomplete
framebuffer)
Mesa: 1 similar GL_INVALID_FRAMEBUFFER_OPERATION errors
(repeated several times)

Mesa: User error: GL_INVALID_ENUM in
glRenderbufferStorage(internalFormat=GL_SLUMINANCE8)
Mesa: User error: GL_INVALID_ENUM in
glRenderbufferStorage(internalFormat=GL_SLUMINANCE8_ALPHA8)

(the first three lines repeated several times again)

I think those errors could explain the incorrect rendering. Which driver was
the apitrace captured with? Does the same problem occur when running the
application with radeonsi directly?