Intermittent lockup HRR216

HRR216K9VKAA
MZCG-9726595

I’ve replaced the belt and adjusted the drive cable
Intermittently the mower stops “propelling”, does not free wheel, its locked up.
Pull it backwards a bit reengage drive and off it goes u til the next lockup.
No sure what to do next, help appreciated

a lot of those mowers use a clutch system at the outside of each wheel. If so it needs servicing annually, which rarely happens. Also if so, those clutches (called axle keys) handle the freewheeling and drive. Parts 3 and 4 in picture. I am guessing that the whole assembly needs cleaning and lubing periodically. My toro, which is similar does.

Tore the wheel assembles apart clean and lubed everything.
Nothing looked bad, some wear on the teeth of one drive pinion.
Took top off transmission, oil is a bit shiny, swirled a magnet through the fluid, no chunks.
Did find the spring that provides tension to the transmission with one end disconnected, reconnected and reassembled.

Will see what happens

Let us know. The keys have to move freely and over time the grease can solidify and dirt get in, making the keys fail to work properly. Also the spring you found loose might have changed belt tension.