Verstappen qualified and finish sixth in Monaco, while team-mate Sergio Perez was eliminated in Q1 and then caught up in a lap-one accident.
It followed an already challenging weekend at Imola, where Verstappen and Red Bull had to dig deep to fix their car handling issues between free practice and qualifying, and the Dutchman was just able to keep McLaren's Lando Norris at bay in the race.
Miami, where Norris won, and Melbourne were also weekends where Red Bull looked less comfortable than it had been over the past 18 months.
Monaco has further exposed a weakness on kerbs and bumps that costs the RB20 more performance than other teams.
That weakness has largely been carried over from last year, but the RB19's dominance meant it was able to compensate for it elsewhere on almost every circuit, other than a fraught weekend in Singapore.
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But the fact that Red Bull still hasn't been able to solve its struggles has also sent some alarm bells ringing because, according to Verstappen, that shows the Milton Keynes-based squad still doesn't understand how to fix it.
"It is a fundamental problem, so it is not something that will be fixed within weeks," Verstappen said.
Asked by Autosport if that means it is an inherent chassis problem that won't be rectified before 2025, he replied: "We need to understand what it is, because we clearly don't understand it.
"But we will work hard to find the problem and then try to get rid of it. I don't know if we can do it this year but hopefully for next year."
With Ferrari and McLaren now closing the gap, Red Bull won't be able to get away with less-than-perfect weekends. This also suggests circuits where Red Bull managed to snatch wins last year will now become a more tricky proposition.
Singapore is the obvious one, because Red Bull was completely lost there last year. But next weekend's Canadian Grand Prix in Montreal features another bumpy layout where kerb-riding is important, and which doesn't have the type of high-downforce corners where Red Bull's RB20 could show its muscle.
"There are definitely a few tracks on the calendar that are not ideal for us," Verstappen warned.
"Any track that is bumpy or you have to ride a lot of kerbs, so the street circuits, will probably be a little bit tricky but hopefully by then we have a little bit of understanding of what is going on."
But, equally, the triple world champion believes that circuits where bumps are less of an issue, such as the following race in Barcelona, will still be strong for Red Bull.
"There are also some races that will suit our car again more," he added. "But we know where we have to work on.
"There's one clear direction where I think we're still lacking quite a bit of performance. So if we can fix that, our car will be better in general on every single track."
Additional reporting by Ronald Vording
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