Turns out, captions can only be 1024 characters long

redditbot.py

@@ -225,7 +225,7 @@ async def main():
                                     desc = i['description']
                                     if desc:
                                         to_append += ': ' + desc.strip()
-                                    caplength = 2047 - len(client.parse_mode.parse(text)[0])
+                                    caplength = 1023 - len(client.parse_mode.parse(text)[0])
                                     captext = to_append[:caplength]
                                     if len(captext) >= caplength:
                                         captext = captext[:-1]
@@ -288,7 +288,7 @@ async def main():
                         else:
                             tat = f'<a href="{url}">{zws}</a>{tat}'
                         if pdesc:
-                            caplength = 2047 if pimg else 4095
+                            caplength = 1023 if pimg else 4095
                             caplength -= len(client.parse_mode.parse(tat)[0])
                             captext = pdesc[:caplength]
                             if len(captext) >= caplength: