"Grossness" takes time to grow in the proper environment... warm & wet with ample time is a perfect place. That's probably what happened to your winter stored hose.
I'm currently using a 50' Flexzilla hose... it claims "drinking water safe", BUT it's not NSF certified. To me, it's immaterial because of my filter process mentioned previously. I supplement that with an additional 25' blue hose, which I rarely need except for my filter hookup. The Flexzilla is easy to wind, is lightweight and doesn't kink.
I recommend using lengths of 25' hose screwed together... it's much easier to wrangle than long lengths of typical hose.
Here's a thesis on my sanitation process, and my recommendations...
Drain your hoses as best you can. Screw the ends together. Then store in a dark storage away from sunlight and heat.
If you use your hoses regularly... like at least once a week, just flush a few gallons of tap water through before you hook it up to your filter.
Same goes for your filter. If you use the blue Camco filters, shake the water out when you disconnect, then PUT THE CAPS BACK ON. Again... make sure you flush water through the filter if it's sat any length of time... a couple weeks in heat and IMO you're pushing it... especially if you drink that water... which I DON'T recommend.
Here's how I sanitize everything once a month (or so). First drain the freshwater tank. I put one end of the hose into the gravity fill on the freshwater tank. If you have multiple hoses, connect them all together. Then, before connecting the other end to the tap, I CAREFULLY pour about 3/4 cup of bleach directly into the hose... then connect it to the tap. Quick and easy.
Turn on the water... which flushes the bleach through all the hoses and into the tank. I completely fill the tank... turn on the water pump and run each faucet until I smell bleach. Turn off the pump and let it sit overnight. Then drain... flush the tank, drain. After the second fill of the tank, I turn on the pump and flush the plumbing.
At this point everything is sanitized and ready to use for showers and general use. For drinking it depends on the water source.
To repeat... from this point gravity draining your hoses and storing with ends together in a dark storage compartment should keep them okay for at least a week.
Something you might try for longer term storage is flushing a slightly stronger bleach solution through your hoses. I do this before winter storage... I drain the hoses VERY well at this point... then screw the ends together. Then they're stored in a shed outside in Ohio winter temperatures... anywhere from well below freezing to rarely over 50°F. In spring they're ready for the regular sanitation process... I've NEVER had any mold growth or nasty stuff.