You need to group. The issue is party members seeing events of another party member who operates a pet.
Recount already has special code to take extra information for self into account, so self-handling of pets is easier and in general more robust against combat log issues.
Two things to look for is: Does the SPELL_SUMMON event properly trigger when the pet is summoned, and does the pet have the right flags associated with it, when it does create combat-log relevant data (such as attacking or taking damage).
The right flags should be group, friendly and player-controlled. It's bugged if it shows hostile, ungrouped etc.
If events trigger multiple times that only should trigger once, that is also an issue that has emerged recently.
81x Recount-v4.1.0 release\Tracker.lua:907: bad argument #1 to "bit_band" (number expected, got string)
<in C code>
Recount-v4.1.0 release\Tracker.lua:907: in function "CheckRetentionFromFlags"
GuessedAbsorbs_Mode.lua:225: in function "?"
Ace3-r1023\CallbackHandler-1.0\CallbackHandler-1.0-6.lua:147: in function <Ace3\CallbackHandler-1.0\CallbackHandler-1.0.lua:147>
<string>:"safecall Dispatcher":4: in function <string>:"safecall Dispatcher":4
<in C code>
<string>:"safecall Dispatcher":13: in function "?"
Ace3-r1023\CallbackHandler-1.0\CallbackHandler-1.0-6.lua:92: in function "Fire"
Ace3-r1023\AceEvent-3.0\AceEvent-3.0-3.lua:120: in function <Ace3\AceEvent-3.0\AceEvent-3.0.lua:119>