Predator and CL did not provide any possible suspects.
Using Code Search for the file, "dictbe.cpp" assigning to the concern owner.
@jshin -- Could you please look into the issue, kindly re-assign if this is not related to your changes.
Thank You.

Testcase has an invalid UTF-8. 

𧻓㌛蟟m 

followed by 0xE8. 

Given that only valid UTF-8 or UTF-16 is fed to the API in question in Chromium/Blink, the risk woouldn't be that high.  Anyway, the ICU code in question needs to be hardened. 

The byte sequences of the minimized test string :
ef ab 97 e3 8c 9b e8 9f  9f 6d e8

3 characters (of 3 bytes in UTF-8) followed by 'm' and followed by 0xE8. 

For more information, please see https://chromium.googlesource.com/chromium/src/+/master/testing/libfuzzer/reference.md.

The link referenced in the description is no longer valid.

(bulk edit)

ClusterFuzz has detected this issue as fixed in range 525156:525177.

Detailed report: https://clusterfuzz.com/testcase?key=5000525501431808

Fuzzer: libFuzzer_icu_break_iterator_fuzzer
Job Type: libfuzzer_chrome_asan_debug
Platform Id: linux

Crash Type: ASSERT
Crash Address: 
Crash State:
  prev.elementAti(t_boundary.elementAti(numBreaks - 1)) == 0
  icu_59::CjkBreakEngine::divideUpDictionaryRange
  icu_59::DictionaryBreakEngine::findBreaks
  
Sanitizer: address (ASAN)

Regressed: https://clusterfuzz.com/revisions?job=libfuzzer_chrome_asan_debug&range=452151:452185
Fixed: https://clusterfuzz.com/revisions?job=libfuzzer_chrome_asan_debug&range=525156:525177

Reproducer Testcase: https://clusterfuzz.com/download?testcase_id=5000525501431808

See https://chromium.googlesource.com/chromium/src/+/master/testing/libfuzzer/reference.md for more information.

If you suspect that the result above is incorrect, try re-doing that job on the test case report page.

ClusterFuzz testcase 5000525501431808 is verified as fixed, so closing issue as verified.

If this is incorrect, please add ClusterFuzz-Wrong label and re-open the issue.