Did some digging into Q plane pic post, following up on Anon's research it was a United Airlines B787-9.
(It is definitely not a BA cabin as some claimed earlier!)
The only domestic flights operated by UA using a B787-9 are San Francisco-Houston or Los Angeles to Houston, both return.
The only UA flight yesterday I could find that was suspicious was UA832 IAH-LAX using aircraft reg N26967, which is a boeing 787-9 series.
https://www.flightradar24.com/data/flights/ua832
What is suspicious is the flight returned to the gate after departure and then was delayed until later in the evening.
From United Airlines flight status page:
http://unitedairlinesflightstatus.com
(UA) UNITED AIRLINES 832
Flight: (UA) United Airlines 832
Departure Date: Sat 29-Sep-2018
Route: This is a multi-segment flight.
Click on the flight links below to view detailed status information.
Flight Origin Destination Departure Arrival Status
UA 832 FLL IAH 1:58 PM 3:40 PM Landed
Delayed
UA 832 IAH LAX 6:15 PM 7:36 PM Diverted
UA 832 IAH LAX 6:15 PM 7:36 PM Landed
Delayed
Flight radar missed out this returned to gate data and it simply records the flight as leaving Houston late and arriving late into Los Angeles
Original schedule departure time was 1815 local arriving Los Angeles 1936 local.
Expertflyer.com (for which you need an account) gave the reason for the delay as 'maintenance'
It is possible the aircraft returned to the gate as there was a mechanical fault and then carried on late or there may be more to it.
Expert flyer information:
UA 832 Landed FLL
Term: 1
Gate: C1
Scheduled: 29/09/18 13:58
Estimated: 29/09/18 14:39
Actual: 29/09/18 14:39
73% / 29m IAH
Term: C
Gate: 12 Baggage: C8
Scheduled: 29/09/18 15:40
Estimated: 29/09/18 16:18
Actual: 29/09/18 16:18
UA 832 Diverted to IAH IAH
Term: C
Gate: 7
Scheduled: 29/09/18 18:15
Estimated: 29/09/18 18:12
Actual: 29/09/18 18:12
81% / 23m LAX
Scheduled: 29/09/18 19:36
Estimated: 29/09/18 18:39
Actual: 29/09/18 18:39
UA 832 Landed IAH
Term: C
Gate: 7
Scheduled: 29/09/18 18:15
Estimated: 29/09/18 22:30
Actual: 29/09/18 22:30
81% / 23m LAX
Term: 7
Gate: 72A Baggage: 1
Scheduled: 29/09/18 19:36
Estimated: 29/09/18 23:40
Actual: 29/09/18 23:40
Comments:
0832/29SEP
P FLL/OUT 239P L00.41 EST OFF 258PAWAITING FLT
P FLL/OFF 252P
P IAH/ON 413P
P IAH/IN 418P L00.38 ☨
P IAH/OUT 612P E00.03 EST OFF 629P
P IAH/RR 639P
P IAH/OUT 1030P L04.15 EST OFF 1047PMAINTENANCE
P IAH/OFF 1046P
P LAX/ON 1131P
P LAX/IN 1140P L04.04 ☨☨
P LAX/IN 1140P L04.04 ☨
D HDQ/IAH LAX PROT UNDER GG CN2 X76
SKED FLL ORIG 158P GTD C1 SHIP 4101
IAH 340P 615P GTA C12 GTD C7 SHIP 3967
LAX 736P TERM GTA 72A