Thirty seconds at f8 seems quite a long time to make a 3½" x 5" print, even with a filter.
The developer is the most likely culprit. Was it freshly mixed? Was it the right strength? A remote possibility (I've done it myself) is that the paper was upside down when exposed.
If it hasn't happened before under the same conditions, it's unlikely to be fogging from the safelight, although as it's half a sheet, it might have had some inadvertent pre-flashing the last time it was out of the box.
Is there something unusual about the negative? Filter 5 suggests that it has very low contrast.
There are ways of intensifying negatives, some riskier than others. I've used chromium intensifier, which can be repeated for greater effect, but it increases grain and can ruin the neg permanently. It's a bleach and re-develop system. Selenium is often suggested, but I've only seen about half a grade improvement, although others report more. It doesn't damage the neg, but both are irreversible.
It would be possible to scan the neg, adjust it on screen and them output a second corrected neg, as alternative printers do, but this does look like a lot of work, when the image could be printed directly from the scan.
Assuming it's a large format neg, it would be possible to make an unsharp mask*, but reversed to be a second negative and bind the two together to improve density.
Is it a valuable negative?
*A footnote for the digital generation. Although Unsharp Mask in Photoshop comes under the Sharpen menu, it was originally devised as a way of reducing contrast in wet printing, by combining the original negative (or transparency) with a thin contact print, made on film (which would be a positive). Because of the difficulty of getting absolutely perfect registration, and to avoid destroying micro-contrast, the mask was made slightly blurred by interposing a sheet of glass when the contact was made. The sharpening effect came from the narrow halo created by the blur, and was a bonus. In Photoshop, the filter has no effect on overall contrast, but it does create a halo if overused.