Ken, it shows this confounded instrument is still on your mind. That's a good thing. (Well, if you wanna be a fiddler)
Y'know, I still get diagonal on occasion. Happens when I'm in a hurry to play something. Or when I'm tired and my posture goes to h@ll. Without doing a whole video on a matter that'll be addressed hopefully by your instructor, I'll say be more mindful of you posture and grip. Get very intentional and repetitive on the posture and bow hold that yields good results.
At the risk of starting a whole mish-mash, do you have your thumb under the frog, for your grip? It starts with the grip, but the whole arm is a linkage. Like shooting pool over your shoulder.

This is a common issue, and even advanced players check themselves sometimes!

I think standard teacher advice is to watch your bow in a mirror when playing, and try to keep it going straight (I.e. parallel to bridge, not fishtailing around). Your arm/wrist/hand will learn the path needed, via the visual feedback. Try just bowing simple straight, long bows (not playing a tune) and really focusing on the track of the bow. COncentrate on how it feels to bow straight, so it can soak into your muscle memory...

( I don't think it could be rosin unless you have zero rosin or huge amounts of it or something? ALso is your bow tightened so that the stick still has a slight gentle curve to it...standard tightness?)

The bow needs to move in a straight path but unfortunately all our joints move in curved radii. No one joint can only execute the bows path completely, they all have to compensate and counteract for each other to move in a straight line. It's a coordination thing - shoulder, elbow, wrist, fingers. The mirror will guide the coordination. The up and down of the wrist is important. Eventually the correct feel gets imprinted but its good to check with the mirror regularly. Some people watch where the bow is contacting the string but it gives me eye strain LOL. Getting control of the contact point (distance of hair from bridge) is crucial for consistant tone but lots of fine players are all over the place!

Keeping the bow on a straight path requires an arm path that isn’t straight, more of a C shape. As the bow gets to the tip, the wrist should be further away from the body, and as it reaches the frog, it should be closer.

If the bow is moving sliding down over the fingerboard, also make sure the scroll isn’t pointing downward. Gravity will send the bow off course if the scroll drops. This is a common beginner error.

The mirror is an indispensable tool for checking these things.

In a nutshell - its you. It not the rosin or strings or set up or bridge. It more muscle memory stuff, just like hitting the notes true and applying the correct pressure with the bow. Its all you. Fiddle is rife with needed to be learned muscle memory tasks and nothing is a substitute for practicing correctly. No short cuts, no magic pill or powder. Just time and repetition doing it right. Sorry!