Hi,
Can you send a bug report in unity?
(goto : playmaker/tools/submit bug report)
add a link to this topic.
Also maybe you can make a video showing your issue.
Before you try anything below make a backup of your project !Some other things you can try is update playmaker. (1.8.5 at the moment)
Update unity to 5.6.3
If you want to keep 5.5.0f3 you can rename the unity folder(where unity is installed) to for example "Unity 5.5"
then you will have 2 versions after installing 5.6.3 (i have 4 versions myself on my pc
)
are you on windows/mac/linux ?