When OnDemand is set to 'true' with the new OnDemand implementation in 1.5.0-1 to keep the biome maps loaded it causes all the biome maps for all custom bodies to be loaded at once which seems to cause a temporary freeze before going into the Map View from Flight mode.

To replicate, install KSP, MM, Kopernicus, MFI and a basic planet pack with OD enabled (OPM) and then spawn a vessel and toggle Map Mode from Flight Mode on the launchpad. The game should freeze temporarily.

The logs suggest that all the biome textures are being loaded at once causing the delay.