I created the bot using aiogram 3.4.1 and it worked well. I left the project for two months and returned to it recently. When calling any menu, the bot gives an error:

aiogram.exceptions.TelegramBadRequest: Telegram server says - Bad Request: can't parse entities: Unsupported start tag "" at byte offset

Next are lines about dispatcher errors:

Traceback (most recent call last):
  File "/Users/.../lib/python3.10/site-packages/aiogram/dispatcher/dispatcher.py", line 309, in _process_update
    response = await self.feed_update(bot, update, **kwargs)
  File "/Users/.../lib/python3.10/site-packages/aiogram/dispatcher/dispatcher.py", line 158, in feed_update
    response = await self.update.wrap_outer_middleware(
  File "/Users/.../lib/python3.10/site-packages/aiogram/dispatcher/middlewares/error.py", line 25, in __call__
    return await handler(event, data)
... and more

I have tried other versions of aiogram. I changed the quotes in the menu item definitions to single ones. Nothing helped. Search didn’t help me too.

Please help me to understand what the problem is it, because the bot worked well before, and I don’t want to completely rewrite it.

main.py

from aiogram import Bot, Dispatcher
from aiogram.enums import ParseMode
from aiogram.fsm.storage.memory import MemoryStorage
from aiogram.client.bot import DefaultBotProperties

async def main() -> None:
    bot = Bot(API_TOKEN, default=DefaultBotProperties(parse_mode=ParseMode.HTML))
    dp = Dispatcher(storage=MemoryStorage())
    dp.include_router(common.router)

    await bot.delete_webhook(drop_pending_updates=True)
    await dp.start_polling(bot)

if __name__ == "__main__":
    asyncio.run(main())

common.py

from aiogram import F, Router
from aiogram.filters import Command
from aiogram.fsm.context import FSMContext
from aiogram.types import Message

from handlers.keyboard import start_keyboard
from handlers import add_hand
from handlers import manage_hand
from handlers import count_hand
from handlers import service_hand

from config import admins

router = Router()

router.include_router(add_hand.router)
router.include_router(manage_hand.router)
router.include_router(count_hand.router)
router.include_router(service_hand.router)

@router.message(F.from_user.id.in_(admins), Command(commands=["start"]))
async def cmd(message: Message, state: FSMContext):
    await state.clear()
    keyboard=start_keyboard()
    await message.answer(
        text="Choose action",
        reply_markup=keyboard
    )
    
@router.message(Command(commands=["cancel"]))
@router.message(F.text.lower() == "back")
async def cmd(message: Message, state: FSMContext):
    await state.clear()
    keyboard=start_keyboard()
    await message.answer(
        text="Choose action",
        reply_markup=keyboard
    )

keyboard.py

from aiogram.types import ReplyKeyboardMarkup, KeyboardButton

def make_row_keyboard(items: list[str]) -> ReplyKeyboardMarkup:

    row = [KeyboardButton(text=item) for item in items]
    return ReplyKeyboardMarkup(keyboard=[row], resize_keyboard=True)

def start_keyboard():
    kb = [
            [
                KeyboardButton(text="Add"),
                KeyboardButton(text='Manage'),
                KeyboardButton(text="Count"),
                KeyboardButton(text="Service")
            ],
        ]
    keyboard = ReplyKeyboardMarkup(
        keyboard=kb,
        resize_keyboard=True,
        input_field_placeholder="Choose action"
    )
    return (keyboard)