I added the SSL certificate through DreamHost which automatically adds https to the URL. It always defaults to it, I just hadn't updated the URL to https here on DBTech. I've looked at the links you provided and it's all very baffling. While it looks like it might not be related to Classifieds specifically, it's only when I try to submit listings that I get the problem so far and it seems to have only happened since a recent Chrome update. I'll let you know if it happens elsewhere too. (In which case I'll have to start recommending Firefox which is a pain for me too since I use Chrome almost exclusively.)
I do run quite a lot of mods (many by you, haha), I must admit, but since you asked I may as well say 'em all. Here's a list:
BF - Easy Pages v1.3.9
Bluepearl Skins - Social Page Icons v1.0.0
DragonByte Tech: Advanced Post Thanks / Like (Pro) v3.3.1pl1
DragonByte Tech: Classifieds (Lite) v1.1.17
DragonByte Tech: InfoPanels (Pro) v2.2.1
DragonByte Tech: Postbit Tabs (Pro) v1.1.4
DragonByte Tech: Raffles (Lite) v1.2.2
DragonByte Tech: Triple Triad Pro v1.1.1
DragonByte Tech: vBActivity & Awards (Pro) v3.2.2
DragonByte Tech: vBArcade (Lite) v2.0.2
DragonByte Tech: vBCredits II Deluxe (Lite) v2.1.1
DragonByte Tech: vBNotifications v1.0.5
DragonByte Tech: vBShop (Lite) v3.5.3
e360 Always Show Your Signature v.1.0.0
Easy Mod Tools v4.2.0
eBay Partner Network Links by ForumSetup.net v1.0
GeekyDesigns Default Avatar v2.0.3
JB: Enhanced Poll Checks v1.0.0
KeyCAPTCHA v3.7.0
Last Poster Avatar v1.1.1
Last Seen Online (Postbit) v2.0
MarkFL: Additional Thread Tools v1.3.2
MarkFL: Spoiler BBCode v1.3
MarkFL: Vote On Polls In Closed Threads v1.0
ModernvB - Community News Letter v1.6.3Pv4
Random Thread v1.0
Sakera's Hide Poll Result v1.5
Tapatalk v5.6.11
Thread Thumbnail v1.0
Usergroup Allow HTML v4.001
XenForo Style Avatars v1