For some time I have been running into the problem where uploaded worksheets that are inlined into a Mapleprimes post get gridlines shown, even when they are not specified or shown in the original worksheet. This is a problem because quite often the gridlines make an inlined plot unattractive.
I believe that Mapleprimes uses some version of MapleNet as a mechanism for inlining uploaded worksheets.
It seems that the Standard GUI and/or MapleNet have special handling for gridlines in the sense that they actually distinguish between PLOT structures generated without the `gridlines` option versus those created with `gridlines=false`. I believe that this has something to do with the persistence of various plot qualities in an output region which (perhaps for historical reasons?) allow re-execution of a plot input command to produce a plot output rendering that remembers whether gridlines are visible.
If the second plot below does indeed get rendered here in Primes without gridlines visible then one workaround is evident: adding `gridlines=false` instead of omitting the option.
I'll submit a bug report against MapleNet.