random issues when using partcombine - v2.20.0

[Eby Mani]

When using partcombine, some beams are not printed or chords are not combined 
properly at all, e.g. attached screenshot.

How to fix this ?.

thanks,

%%%%%%%%%%%%%%%%%%%%%%%
\version "2.20.0"

global = {
  \numericTimeSignature
  \key d \major
  \time 3/4
}

rightOne = \relative c' {
  \global
fis4. fis8 e e %bar
\time 4/4
<a cis>4. <g b>8 <fis a> fis <g b> r %bar %%%missing beaming - 3rd beat.

}

rightTwo = \relative c' {
  \global
d4. d8 b cis %bar
\time 4/4
d2 cis8 d d r %bar %%% 3rd beat chord not combined with rightOne.
}

leftOne = \relative c {
  \global

  \once \partcombineApart r8 fis a a g4 %bar
\time 4/4
<g d>2 a8 <b fis> \partcombineApart r <b g> %bar %%%missing beaming - 3rd beat.

}

leftTwo = \relative c {
  \global
a4. a8 a4 %bar
\time 4/4
g2 a8 b <e b e,>4 %bar %%%missing beaming and chord not combined with leftOne - 
3rd beat.

}


Rhand = << \partcombine \rightOne \rightTwo >>
Lhand = <<  \partcombine \leftOne \leftTwo >>

pianoPart = \new PianoStaff \with {
  instrumentName = "Piano"
}
<<
  \new Staff = "right"  {
    \set Staff.printPartCombineTexts = ##f

    \Rhand }

  \new Staff  = "left"  {
    \set Staff.printPartCombineTexts = ##f

     \clef bass \Lhand }
  >>

\score {
<<
    \pianoPart
>>
  \layout { }
}