If a map takes more than a few seconds to load, one of three things is usually going on.
Map is large
Maps with 100+ stages or 50+ runs take longer to render. Consider archiving old runs (they stay in the DB but don't load with the map) or splitting a mega-map into a Process Chain of smaller maps.
Browser is old
MapVS uses modern browser APIs (offscreen canvas, structured clone, indexedDB). Safari before 16 and any Firefox before 100 will be noticeably slower. Update your browser.
Network is slow
The initial map load is ~500 KB - 2 MB depending on stage count. On a slow connection this shows as a lag before the canvas appears. Once loaded, interactions are entirely local.