Route rewriting itself when changing start and stop points - Can the route be locked?

I have been routing and riding chunks of the King Alfred's Way. I used https://cycle.travel/map/journey/577335 as a base map and was able to easily modify and study the route using PC and app, all brilliant. My problems began with adding markers - disappearing not saving etc- I believe this may have been addressed according to the forum. 

Then I noticed (using PC), when changing the start and stop points near to my location near Wantage, the route suddenly started modifying itself to a subtlety new route -its easy to miss what's happened until you're out cycling the route. I think Richard has explained previously that waypoints converted onto a  route map in particularly areas such as the ridgeway without geographic points such as roads can get misinterpreted. I'm not sure what's happening - Can the map be locked/unlocked? ( I know you can toggle "add points" and off ) Of course you can repair the route with added points or use "Direct". Locking all the route or better still parts of the route would be great (unless I've missed this feature). Currently I'm saving multiple versions of the map so I can revert if the rerouting gets out of hand.

I found a similar but unrelated problem using the android version of the app. When trying to check the map in the field I would sometimes clumsily add a point while manipulating zoom etc this would often lead to a rerouting. Again would a lock feature improve this? If I noticed this happening I tapped undo or reopened the map - if I missed it I ended up going the wrong way!

Clearly locking the route would also mean the need to unlock the route for editing -  I accept some may find this annoying