Jumping in here... building on the earlier suggestion, I have been extremely satisfied with the transition to lithium-ion power for my professional Nikon bodies. The Godox V1-N Round Head Flash for Nikon has proven itself to be a reliable workhorse for wedding coverage and I have no complaints. Unlike the older SB units that chug along on AAs, the V1 stays consistent until the battery is nearly empty. It integrates perfectly with the D850 for HSS without those communication glitches you're experiencing. One quick tip for reliability: check for the latest firmware updates via the Godox G3 software before your Chicago gig. It solves most communication issues people report. If the round head isnt your thing, the Godox V860III-N TTL Li-Ion Flash for Nikon offers the same performance and battery life in a standard form factor, keeping you well under that 450 dollar limit.

Agreed on Godox, but watch the price. I'd suggest the Godox V860III-N TTL Li-Ion Flash for Nikon instead. I once had an old unit fail mid-aisle, so just be careful with thermal cutoffs.

I definitely agree that moving away from that older tech is the right call for a pro body like the D850. In my experience, those older units really struggle with the communication protocols on the newer Nikon sensors, especially when you start pushing the frame rate during a fast-paced bridal shoot. Over the years, I have tried many different speedlight configurations, and the most common failure point I see is the internal capacitor not keeping up with the High Speed Sync demands. One small point I would add to the conversation is that you really need to look at the battery architecture. Standard AAs just dont have the discharge rate required for consistent HSS at a wedding. If you are shooting in a bright Chicago venue and need that fill light, you need a unit that utilizes a dedicated lithium-ion pack. It makes a world of difference for those recycle speeds you mentioned. I have found that lithium-powered units stay consistent right until the battery hits about ten percent, whereas those old SB units start slowing down the recycle time as soon as the AAs hit half capacity. For a professional gig where you cannot afford to miss a single frame, that consistency is basically non-negotiable. It really saves your sanity when the pressure is on.