When a small graph is drawn, for example several marks horizontally, a spinning spinner is visible at the edges.
.mw-graph has this: background-image: url (/w/extensions/Graph/includes/ajax-loader.gif?b3af8); and border: 1px solid transparent;
When there is something short on the graph and #tag:graph has "height": less than 47, then inside this border which is transparent is visible loader.gif and border flashes with gif animation

one mark and spinner flashes inside the border around the mark

"height":40 and the top and bottom of the spinner remains

the spinner itself
This is not visible in Special: GraphSandbox since there is no .mw-graph but visible in pages and in Special: ExpandTemplates. Spinner was definitely not visible in 2018.
.mw-graph {background-clip: padding-box;} (or content-box) can fix border or border can be replaced with margin/padding