The Jungle Movie takes place in a reimagined late-1990s continuity.
Resuming only about a year after the main series ended (which was a quintessential fixture of The '90s era), The Jungle Movie takes place in an Ambiguous Time Period in which technology that only became ubiquitous later in the early twenty-first century has already become widespread (such as smartphones, laptops, and other portable electronic devices), displacing the beeper industry that was "Big Bob" Pataki's bread and butter (which nevertheless remains just barely viable enough that "Big Bob" is able to keep his store open while retaining the increasingly-obscolescent beepers as the primary product sold there). Meanwhile, airport security is much more lax than it is following 9/11, with families accompanying their children on the airport tarmac seemingly without having to have undergone intensive security screening in order to do so and Grandpa Phil even following Arnold onto the plane (despite being promptly escorted off when he was delaying its takeoff), after which he and Grandma Gertie hijack an airstairs vehicle without any onscreen consequences (the latter of which was admittedly probably just for comedic effect). However, this is later followed up by Grandpa and Grandma attempting to "hitchhike" to San Lorenzo on the airport tarmac without any airplane ticket (which the Transportation Security Administration would almost certainly require them to have to get past the terminal these days), "Big Bob" and Miriam driving their Humvee right onto the tarmac to reach their rented plane (also seemingly without having to undergo much, if any, security screening), and Abner and the snake that was stalking him boarding a flight from San Lorenzo to Hillwood without getting any tickets in advance (okay, that last one was probably just meant to be funny as well).Suzie finally left Oskar and moved out prior to the events of the movie
Hence why she's absent from all the scenes taking place at the boarding house.Confirmed During Craig Bartlett's 2018 Reddit AMA
Arnold and the gang are in fifth grade by the time "The Journal" takes place
It happens in October, seeming to indicate that another year has gone by and Arnold is not shown in school in this episode. Just something I came up with to try and make the timeline work a bit better. The Sleep Sickness just puts people in short-term comas
Or at least it does now Miles and Stella did just enough to stop it from being deadly. This also explains how they could be alive despite contracting the illness themselves, the coma comes and goes for an unspecified amount of time before it starts up again. This is a fairly good reason to keep them from going home and possibly spreading the illness. Scheck would've saved Big Bob's Beeper Emporium had he managed to tear down the community.
Unlike Big Bob, he would've realized it on time beepers would become obsolete and changed it into a smartphone emporium. Scheck and Vermicelli, intentionally or not, would have actually honored the promise of making Big Bob rich.