Posted this on Facebook. Turns out I'm not the only one.
Link to post: https://www.facebook.com/groups/p3dgroup/permalink/1363947666975409/?comment_id=1364999070203602&reply_comment_id=1365009820202527&notif_t=group_comment_reply&notif_id=1497580559292182

This first occurred to me on my second 777 flight on P3Dv4 when I landed at CDG. Speed was 137, Flaps 25 and autobrakes set to level 1. I was landing on 26L. FPM according to ProjectFly was -195. Upon touchdown, I began the normal rollout procedure. Reverse thrust, maintain the centre line etc. When suddenly my aircraft began to slow rapidly until it came to a full stop. I have the gear page open whenever I and taking off or landing to monitor my landing gear. It showed that all main gear were at 10.0 degrees and tires deflated. Picture can be found on the post. Follow the link above.

From what I have read on the Facebook post, this must be a bug and not a mechanical issue with the aircraft.

Hi,

The best info you can get is on the forum here.

Please do a search on the forum as this has been posted several times already.
As a starter, here are two links but they are not the only ones:

And by the way, please sign your posts with full names as required by forum rules.
Before calling it a bug, check the calibration of your hardware. They are not the same in P3D v4 as in the v3 so you have to do it again.

Also if you are using fsuipc 5, do a new profile from scratch. Profiles imported from fsuipc 4 may not work properly.