graphics3d – Severely distorted plotting in V12.1 but works in V12

The following code can plot a 3D surface (the plot1) and also makes a row of two plot1s using Grid. It works fine in V12 and we can save the .nb archive.
Nevertheless, either open this file saved in V12.1 or answering it in V12.1, I find that (Mac or Windows)

Plots V12
enter the image description here

Plots V12.1
enter the image description here

{ticksize, labelsize, imagesize} = {27, 31, 500};
viewpoint2 = {3, -2.14, 0.3};
frametick = {{-0.4, 0, 0.4}, {-0.05, 0, 0.05}, {0, 0.06}};
labellst = {{"X", {0.21, 0.09}}, {"Y", {0.83, 0.1}}, {"Z", {0.06, 
     0.63}}, {"4", {0.48, 0.93}}};
insetlst = 
  Table(Inset(
    Style(ToString(labellst((i, 1)), TraditionalForm), labelsize), 
    ImageScaled(labellst((i, 2)))), {i, Length(labellst)});
boxmax = {0.505, 0.0697, 0.0737}; boxmin = {-0.505, -0.0697, -0.002};
plotpart = 
  ListPlot3D(data1, PlotRange -> Transpose({boxmin, boxmax}), 
   PlotTheme -> {"Grid", "Business"}, Ticks -> frametick, 
   TicksStyle -> ticksize, LabelStyle -> Directive(labelsize), 
   Epilog -> insetlst);
plot1 = Show(plotpart, AspectRatio -> 1/2, ImageSize -> imagesize, 
  ViewPoint -> viewpoint2)

(*plotall=Row({plot1,plot2},FrameMargins(Rule)None,ImageMargins
(Rule)0)*)
plotall = Grid({{plot1, plot1}}, Spacings -> 0)

The data is

data1 = {{-0.4993746088859545`, -2.871131262989668`*^-21, 
    0.024999999999999998`}, {-0.46502003012445886`, 
-0.0020365099189641233`, 
    0.02767503529165532`}, {-0.37976786767106513`, 
-0.0072219052560367316`, 
    0.034493094291508666`}, {-0.27272129708054105`, 
-0.014073090255452649`, 
    0.04351035998591313`}, {-0.15172727596503274`, 
-0.022062857310713998`, 
    0.05399935908925925`}, {-0.001934268375951016`, 
-0.02932156592912235`, 
    0.06326986376188234`}, {0.1486679556704227`, 
-0.027637094744339886`, 
    0.060222191883146356`}, {0.2531835491271039`, 
-0.02287954314463927`, 
    0.05338442336015307`}, {0.3235345805552881`, 
-0.018521344515455854`, 
    0.04738188484102162`}, {0.3712267296134156`, 
-0.014984732307856194`, 
    0.042657088215814314`}, {0.40392868331802423`, 
-0.012209173573874734`, 
    0.03904710049949488`}, {0.42666448249221317`, 
-0.01005076182264755`, 
    0.036309848903034306`}, {0.4427177333308907`, 
-0.008370317874102943`, 
    0.0342305307661711`}, {0.4542423182844073`, 
-0.007052673907610944`, 
    0.03263951073630112`}, {0.4626638959626358`, 
-0.006007215582873967`, 
    0.03140801550699416`}, {0.4689404841250125`, 
-0.005163512825929755`, 
    0.030439161535130065`}, {0.47373137765059126`, 
-0.004466278762901273`, 
    0.029659292801596567`}, {0.47750787274503637`, 
-0.0038709053090247593`, 
    0.02901084048669347`}, {0.48062739503568486`, 
-0.00333988972991638`, 
    0.028446819809153142`}, {0.48338346291017986`, 
-0.0028403215123981723`, 
    0.027926960333316295`}, {0.486035173383759`, 
-0.002342931505073544`, 
    0.027415891529632103`}, {0.4888085518905259`, 
-0.001824102826062602`, 
    0.02688482946970072`}, {0.49184621274791623`, 
-0.0012739045948531953`, 
    0.026320006092917847`}, {0.49506901692813593`, 
-0.0007149871269194862`, 
    0.025742890226662134`}, {0.4979458510840051`, 
-0.00023406751827959705`, 
    0.025243684912488552`}, {0.4993623655791132`, 
-1.9949808358748177`*^-6, 
    0.025002078589007895`}, {-0.47979692493084386`, 0.`, 
    0.024999999999999998`}, {-0.40395960201159664`, 0.`, 
    0.024999999999999998`}, {-0.3006841777318337`, 0.`, 
    0.024999999999999998`}, {-0.18376769373189383`, 0.`, 
    0.024999999999999998`}, {-0.043016130653344524`, 0.`, 
    0.024999999999999998`}, {0.11546221731178323`, 0.`, 
    0.024999999999999998`}, {0.2308072706363814`, 0.`, 
    0.024999999999999998`}, {0.30844525323293653`, 0.`, 
    0.024999999999999998`}, {0.3609549883270275`, 0.`, 
    0.024999999999999998`}, {0.39684825595458967`, 0.`, 
    0.024999999999999998`}, {0.4217121506402877`, 0.`, 
    0.024999999999999998`}, {0.4391981792277835`, 0.`, 
    0.024999999999999998`}};