Maybe coincidence but just in case you are getting pounded by political calls day and night like we are, the recordings are in the neighborhood of 60-75 minutes and I have removed about 110 of them, I eventually got smart and lowered the setting in "Advanced Settings" to limit voicemail to 280 seconds... just a thought since you mentioned the over-sized files, it seems unlikely to me that a normal voicemail would ever go longer than the 280 but you could always adjust it to whatever fits your environment.
The calls come from 80+ numbers so don't bother trying to block them