More than likely your hubs are worn and not engaging properly or they need to be stripped and cleaned re-greased ect but why do you drive with one hub locked?not a good idea.
This is what happened to mine. But one of mu hubs was siezed in lock and the other locked in free position. I did the stupid thing and went beach driving like this stopping every few minutes seeing if i coukd engage the free hub only making it worse stripping the hubs internally. Mechanic cleaned and regreased and somehow got the hub to bite on the last few splines still with teeth on them but recommended a new set. Have the avm hubs ready to put in just finding time to install is a drama.
Take 10 minutes a side. Pull the hub off by removing the 6 hex head bolts and pull it off. Then grab the new hub apply a small amount of grease inside(to much grease will affect how they work aswell) and reinstall.
Will be doing mine this weekend hopefully with the avm units which rwquire me tt remove the circlip holding the cv in etc.
If it's hubs it will be the obvious stripped internal splines of the hub and metal shavings etc. If your swapping genuine hub for genuine hub you won't need the circlip pliers I do t think. Just going from genuine to aftermarket you have to change the whole mounting body
I am just giving the avm aftermarket units a test run. You can get the genuine ones off eBay or from nizzbits for cheaper then the aftermarket ones I purchased at $230 set