QtWebEngine max_old_space_size flag does not work with sandboxing enabled

I have a browser application that needs to load a web page which allocates a large amount of memory (>2GB).  The page will crash unless I run it with flags "--no-sandbox --js-flags=--max_old_space_size=4096".  If I use just " --js-flags=--max_old_space_size=4096", the crash still occurs.

Chrome browser 77.0.3865.75 is able to render the page with just the "--js-flags=--max_old_space_size=4096" flag used.

Crash output:

$./mybrowser -js-flags=-max_old_space_size=4096

<--- Last few GCs --->

[1:0x558bead335f0] 9873 ms: Scavenge 1827.1 (1880.5) -> 1825.9 (1888.0) MB, 22.6 / 0.0 ms allocation failure
[1:0x558bead335f0] 9907 ms: Scavenge 1834.4 (1888.0) -> 1833.2 (1895.0) MB, 22.7 / 0.0 ms allocation failure
[1:0x558bead335f0] 9940 ms: Scavenge 1841.7 (1895.5) -> 1840.5 (1902.5) MB, 22.4 / 0.0 ms allocation failure
[1:0x558bead335f0] 10185 ms: Scavenge 1849.0 (1902.5) -> 1847.8 (1907.0) MB, 234.8 / 0.0 ms allocation failure

<--- JS stacktrace --->
Cannot get stack trace in GC.
Received signal 4 ILL_ILLOPN 7fa385e14215
#0 0x7fa38439af42 <unknown>
#1 0x7fa3824a9f20 <unknown>
#2 0x7fa385e14215 <unknown>
#3 0x7fa384feb2ee <unknown>
#4 0x7fa384feb600 <unknown>
#5 0x7fa3852257bf <unknown>
#6 0x7fa38522be1e <unknown>
#7 0x7fa385237e09 <unknown>
#8 0x7fa385209cac <unknown>
#9 0x7fa385210f38 <unknown>
#10 0x7fa3852116dc <unknown>
#11 0x7fa3851cc942 <unknown>
#12 0x7fa3851cd6ba <unknown>
#13 0x7fa385771476 <unknown>
#14 0x047f9a6043a7 <unknown>
r8: 0000000000000072 r9: 00007fa360000870 r10: 0000000000000160 r11: 0000000000000003
r12: 00007fa3881e3d92 r13: 00007ffc5910e020 r14: 0000558bead33610 r15: 00007ffc5910e840
di: 0000558bead38e40 si: 00007fa3851c8110 bp: 0000558bead335f0 bx: 0000000000000000
dx: 0000000001000000 ax: 000000000000077a cx: 0000000000000000 sp: 00007ffc5910ccf0
ip: 00007fa385e14215 efl: 0000000000010203 cgf: 002b000000000033 erf: 0000000000000000
trp: 0000000000000006 msk: 0000000000000000 cr2: 0000000000000000
[end of stack trace]