Symptoms reflect known TBB-BQM "resource" issue on Hub/SH 3 from 6xx to 613 firmware versions! Easily clarified by enabling alternative BQM ICMP host's: eg email@example.com ..... Normally I'd emphasise the point of ALWAYS browsing the mere 2.3 million posts that include these specific issue.... and many SuperUser escalations since 2015 that have been escalated but can't be published here.
EDIT: I should also add that OP's "tap" may not be optimal but that requires onsite visit to cab AND confirmation that no additional online termination exists on incoming feed..... Enabling alternate ICMP/BQM and Publishing NetworkLog and refreshed Upstream/Downstream stats for this V100 service may also reveal further clues?
Regards Tony "Life is a Binary Inspired Turing Computed Hologram"(don't PM or @Mention me - in case ignoring you offends) DEFROCKED