Unstable display using multislider

Hi everyone

Strange question as usual... I'm wondering, is there a reason why the multislider
in the following patch blinks and sometimes freezes for no reason?

I'm using this for a kind of "score karaoke", to help synchronize musicians with a patch
in a non-invasive manner (unlike click tracks, pedals or others).
Generally I have a fpic object with a music score image behind the slider (which is semi-transparent).

This is really efficient for my kind of work, but yet the quality of visualization seemed to decrease
with Max 7 for some reason, and musicians started to get a bit less comfortable reading the score in live situation.
And of course the problem gets worse as the rest of the patch gets bigger (triggered soundfiles, spatialization, various processes and so on).

I'm afraid this has something to do with priorities on the scheduler.
Just in case, on my config overdrive is on and audio interrupt is off.
I'm using 2 macbook pro (late 2011 and mid 2014) with last versions of Max (still 32bits mode) and Yosemite.

Is there another object that would do the job more accurately?
I really need this display to be the smoothest and more stable possible, and of course accurate regarding time.

Thanks in advance for your help !

Julien

{
    "patcher" :     {
        "fileversion" : 1,
        "appversion" :         {
            "major" : 7,
            "minor" : 2,
            "revision" : 3,
            "architecture" : "x86",
            "modernui" : 1
        }
,
        "rect" : [ 84.0, 129.0, 640.0, 480.0 ],
        "bglocked" : 0,
        "openinpresentation" : 0,
        "default_fontsize" : 12.0,
        "default_fontface" : 0,
        "default_fontname" : "Arial",
        "gridonopen" : 1,
        "gridsize" : [ 15.0, 15.0 ],
        "gridsnaponopen" : 1,
        "objectsnaponopen" : 1,
        "statusbarvisible" : 2,
        "toolbarvisible" : 1,
        "lefttoolbarpinned" : 0,
        "toptoolbarpinned" : 0,
        "righttoolbarpinned" : 0,
        "bottomtoolbarpinned" : 0,
        "toolbars_unpinned_last_save" : 0,
        "tallnewobj" : 0,
        "boxanimatetime" : 200,
        "enablehscroll" : 1,
        "enablevscroll" : 1,
        "devicewidth" : 0.0,
        "description" : "",
        "digest" : "",
        "tags" : "",
        "style" : "",
        "subpatcher_template" : "",
        "boxes" : [             {
                "box" :                 {
                    "id" : "obj-1",
                    "maxclass" : "newobj",
                    "numinlets" : 1,
                    "numoutlets" : 1,
                    "outlettype" : [ "" ],
                    "patching_rect" : [ 40.0, 1.0, 99.0, 22.0 ],
                    "style" : "",
                    "text" : "loadmess 12000"
                }

            }
,             {
                "box" :                 {
                    "id" : "obj-24",
                    "maxclass" : "newobj",
                    "numinlets" : 1,
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                    "outlettype" : [ "float", "int" ],
                    "patching_rect" : [ 52.0, 116.0, 64.0, 22.0 ],
                    "style" : "",
                    "text" : "t f 0"
                }

            }
,             {
                "box" :                 {
                    "id" : "obj-22",
                    "maxclass" : "number",
                    "numinlets" : 1,
                    "numoutlets" : 2,
                    "outlettype" : [ "", "bang" ],
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                    "patching_rect" : [ 52.0, 51.0, 50.0, 22.0 ],
                    "style" : ""
                }

            }
,             {
                "box" :                 {
                    "id" : "obj-18",
                    "maxclass" : "newobj",
                    "numinlets" : 2,
                    "numoutlets" : 1,
                    "outlettype" : [ "float" ],
                    "patching_rect" : [ 52.0, 84.0, 51.0, 22.0 ],
                    "style" : "",
                    "text" : "!/ 1000."
                }

            }
,             {
                "box" :                 {
                    "id" : "obj-14",
                    "maxclass" : "multislider",
                    "numinlets" : 1,
                    "numoutlets" : 2,
                    "orientation" : 0,
                    "outlettype" : [ "", "" ],
                    "parameter_enable" : 0,
                    "patching_rect" : [ 52.0, 290.0, 1236.0, 353.0 ],
                    "setminmax" : [ 0.0, 1.0 ],
                    "setstyle" : 1,
                    "slidercolor" : [ 0.952941, 0.564706, 0.098039, 0.54 ],
                    "style" : ""
                }

            }
,             {
                "box" :                 {
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                    "maxclass" : "newobj",
                    "numinlets" : 2,
                    "numoutlets" : 1,
                    "outlettype" : [ "float" ],
                    "patching_rect" : [ 52.0, 245.0, 83.0, 22.0 ],
                    "style" : "",
                    "text" : "snapshot~ 20"
                }

            }
,             {
                "box" :                 {
                    "id" : "obj-8",
                    "maxclass" : "newobj",
                    "numinlets" : 2,
                    "numoutlets" : 1,
                    "outlettype" : [ "signal" ],
                    "patching_rect" : [ 52.0, 152.0, 64.0, 22.0 ],
                    "style" : "",
                    "text" : "phasor~ 2"
                }

            }
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        "lines" : [             {
                "patchline" :                 {
                    "destination" : [ "obj-22", 0 ],
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                    "source" : [ "obj-1", 0 ]
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            }
,             {
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            }
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            }
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            }
,             {
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                }

            }
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            }
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                }

            }
],
        "dependency_cache" : [ ],
        "autosave" : 0
    }

}