Other than that the triggering actions were related to account creation (createaccount or autocreateaccount) I can't tell what the pattern is, but it seems that some abuse filter log entries are no longer showing up for searches by user
Examples:
enwiki: OakIslandAllianceGroup is missing log
meta: DannyS712 is a bot is missing log
meta: Reviewxiaomiwatch1420 is missing log
simplewiki: Donald Trump for US president is missing log