Rebuilt httpServer using source code from legato-19.07.0/apps/sample/ and installed under red_wp77xx_0.6.0.spk and it now works.
root@swi-mdm9x28-wp:~# cm info
Firmware Version: SWI9X06Y_02.35.02.00 5208b3 jenkins 2020/06/10 00:30:12
...
root@swi-mdm9x28-wp:~# legato version
19.11.2_625c7d1acfd1ca45b2dbe189b4cb1ce7_modified
Thanks again, hope this info will be useful.