nativeexec.exe testing failing with "Possible unsupported evex encoding"

This just happened on a merge to master on the 64-bit Linux CI. You would think a decoding issue would be deterministic: maybe somebody is decoding uninit mem?

https://github.com/DynamoRIO/dynamorio/runs/1566295178

2020-12-16T20:27:19.4268093Z  24/355 Test  #22: code_api|common.nativeexec_exe ...............................***Failed  Required regular expression not found. Regex=[^Not running under DR
2020-12-16T20:27:19.4269135Z calling via IAT-style call
2020-12-16T20:27:19.4269678Z nativeexec\.dll:import_me1\(57\) under DR
2020-12-16T20:27:19.4270366Z calling via PLT-style call
2020-12-16T20:27:19.4270881Z nativeexec\.dll:import_me2\(37\) under DR
2020-12-16T20:27:19.4271401Z calling via funky ind call
2020-12-16T20:27:19.4271901Z nativeexec\.dll:import_me3\(17\) under DR
2020-12-16T20:27:19.4272412Z calling nested native
2020-12-16T20:27:19.4272922Z nativeexec\.exe:print_int\(42\) not under DR
2020-12-16T20:27:19.4273681Z calling cross-module unwinder
2020-12-16T20:27:19.4274159Z before longjmp, 1
2020-12-16T20:27:19.4274554Z after longjmp
2020-12-16T20:27:19.4274981Z calling indirect ret_imm
2020-12-16T20:27:19.4275513Z  -> 40
2020-12-16T20:27:19.4275878Z calling loop_test
2020-12-16T20:27:19.4276278Z Not running under DR
2020-12-16T20:27:19.4276663Z all done
2020-12-16T20:27:19.4276965Z $
2020-12-16T20:27:19.4277258Z ]  0.20 sec
2020-12-16T20:27:19.4277631Z Not running under DR
2020-12-16T20:27:19.4278145Z <Possible unsupported evex encoding.>
2020-12-16T20:27:19.4278886Z calling via IAT-style call
2020-12-16T20:27:19.4279420Z nativeexec.dll:import_me1(57) under DR
2020-12-16T20:27:19.4280121Z calling via PLT-style call
2020-12-16T20:27:19.4280806Z nativeexec.dll:import_me2(37) under DR
2020-12-16T20:27:19.4281336Z calling via funky ind call
2020-12-16T20:27:19.4281867Z nativeexec.dll:import_me3(17) under DR
2020-12-16T20:27:19.4282379Z calling nested native
2020-12-16T20:27:19.4284018Z nativeexec.exe:print_int(42) not under DR
2020-12-16T20:27:19.4284906Z calling cross-module unwinder
2020-12-16T20:27:19.4285387Z before longjmp, 1
2020-12-16T20:27:19.4285798Z after longjmp
2020-12-16T20:27:19.4286212Z calling indirect ret_imm
2020-12-16T20:27:19.4286776Z  -> 40
2020-12-16T20:27:19.4287125Z calling loop_test
2020-12-16T20:27:19.4287541Z Not running under DR
2020-12-16T20:27:19.4287909Z all done