I must admit: rules actually say about player's M/H phase and say about company's M/H phase.
Now try to respect this distinction and try to apply, what rules state about
player's M/H phase.
During your opponent's movement/hazard phase, the number of hazard cards that you may play on one of your opponent's companies is that company's hazard limit.
This is about player's M/H phase, right?
Does it mean that some hazards may be played during player's M/H phase and at the same time not during particular company's M/H phase?
Does it mean that there is any Hazard Limit outside of particular company's M/H phase?
During the movement/hazard phase of your opponent's turn, you may place one card on-guard for each of your opponent's companies.
Does it mean that a hazard player may place an on-guard cards during player's M/H phase and at the same time not during particular company's M/H phase?
Or, maybe, this means that the player's M/H phase is just container for M/H phases of particular companies. That is empty if at the end of Long-event phase a current player does not have any company. And that nothing may happen during player's M/H phase and at the same time not during particular company's M/H phase.
Even in the second case (M/H of player as just container for M/H of companies) what rules say about player's M/H phase looks like mess.
During your opponent's movement/hazard phase, the number of hazard cards that you may play on one of your opponent's companies is that company's hazard limit.
This assumes that there is a hazard limit per company, whereas actually there is a hazard limit per company's M/H phase. If some company has 3 M/H phases in turn (so during player's M/H phase), in each M/H phase has 4 HL, it is possible to play against it 12 hazards (that count against HL) total , all during player's M/H phase. Much more than maximum HL at any given point for that company's any M/H phase.
In other words: the limit "the number of hazard cards that you may play on one of your opponent's companies" could be reached even in first M/H phase of this company.
During the movement/hazard phase of your opponent's turn, you may place one card on-guard for each of your opponent's companies.
Similarly: above does take into account the fact that particular company may take multiple M/H phases.
You may consistently enforce both the limit of "number of hazards per company per
player's M/H phase" and the limit "one on-guard card placed per given company per
player's M/H phase".
Or you may consistently acknowledge error in both cases.
Or you may do not try to be consistent.
Other options... ?