Same problem here but, i suspect, different cause. I am on Kubuntu Trusty and NO Nvidia drivers (Radeon free drivers). Meanwhile, i downgraded Insync to version 1.4.9.37127-trusty_amd64 and all is working again. This is the relevant output when trying to start version 1.5.1:
/usr/lib/insync/QtWebEngineProcess: /usr/lib/insync/libdbus-1.so.3: no version information available (required by /usr/lib/insync/libQt5WebEngineCore.so.5)
libpng warning: iCCP: known incorrect sRGB profile
*** Error in `./insync’: munmap_chunk(): invalid pointer: 0x00007ff4887f6f90 ***
Received signal 6
#0 0x7ff4c721d95f
#1 0x7ff4c5c4f85d
#2 0x7ff4c721de6e
#3 0x7ff4ec9ac330
#4 0x7ff4ebce3c37 gsignal
#5 0x7ff4ebce7028 abort
#6 0x7ff4ebd202a4
#7 0x7ff4ebd2b007
#8 0x7ff4d5e2b588 std::_Hashtable<>::_M_insert_unique_node()
#9 0x7ff4c7828e04 std::_Hashtable<>::_M_insert<>()
#10 0x7ff4c78295ed
#11 0x7ff4c7829c50
#12 0x7ff4c7cc4feb
#13 0x7ff4c7cc7178
#14 0x7ff4c7cc76e2
#15 0x7ff4c5de473f
#16 0x7ff4c659bcfd
#17 0x7ff4c65b6f00
#18 0x7ff4c65b709f
#19 0x7ff4c79af3e3
#20 0x7ff4c721e069
#21 0x7ff4c723fb10
#22 0x7ff4c724056d
#23 0x7ff4c7240857
#24 0x7ff4c7242cb1
#25 0x7ff4c72625ff
#26 0x7ff4c639782b
#27 0x7ff4c6397cdb
#28 0x7ff4c7286308
#29 0x7ff4c72816b0
#30 0x7ff4ec9a4184 start_thread
#31 0x7ff4ebdab03d clone
r8: 3039663666373838 r9: 0000000000000000 r10: 0000000000000008 r11: 0000000000000206
r12: 00007ff4887f6bc0 r13: 0000000000000007 r14: 0000000000000051 r15: 0000000000000007
di: 0000000000000bb1 si: 000000000000102d bp: 00007ff4887f6db0 bx: 0000000000000051
dx: 0000000000000006 ax: 0000000000000000 cx: 00007ff4ebce3c37 sp: 00007ff4887f6a18
ip: 00007ff4ebce3c37 efl: 0000000000000206 cgf: 0000000000000033 erf: 0000000000000000
trp: 0000000000000000 msk: 0000000000000000 cr2: 0000000000000000
[end of stack trace]
Calling _exit(1). Core file will not be generated.