With an L2TP + Ipsec tunnel installed between two mikrotik routers, for some reason the connection of the local machine to vpn PPtP in the external network drops?

Question

Mikrotik

There are two Mikrotiks connected to each other via L2TP + Ipsec and an EoIP tunnel has been raised, an EoIP tunnel on both routers has been added to the bridge. Everything works perfectly.
One of the machines within the network needs to connect via VPN (PPtP) to a remote server. The connection proceeds without errors. But as soon as the data exchange between these machines starts, the vpn connection breaks with an error:
The user established a remote connection that was terminated. When terminated, reason code 829 was returned. When the L2TP server is disabled on Mikrotik, everything works without failures. Where to look in which direction?

Network data:
Office 1:

Public IP: static - ip 31.211.xx.yy
Local IP: 192.168.1.0/24
Пул L2TP: 176.116.10.0/24
Адрес Mikrotik: 192.168.1.1
Адрес VPN PPtP: 88.204.102.194

ipconfig /all machines with vpn connected

Адаптер PPP :

   DNS-суффикс подключения . . . . . :
   Описание. . . . . . . . . . . . . : 
   Физический адрес. . . . . . . . . :
   DHCP включен. . . . . . . . . . . : Нет
   Автонастройка включена. . . . . . : Да
   IPv4-адрес. . . . . . . . . . . . : 10.10.10.184(Основной)
   Маска подсети . . . . . . . . . . : 255.255.255.255
   Основной шлюз. . . . . . . . . :
   DNS-серверы. . . . . . . . . . . : 192.168.0.2
   NetBios через TCP/IP. . . . . . . . : Включен
Ethernet adapter Подключение по локальной сети:

   DNS-суффикс подключения . . . . . :
   Описание. . . . . . . . . . . . . : Сетевой адаптер Hyper-V (Майкрософт)
   Физический адрес. . . . . . . . . : 
   DHCP включен. . . . . . . . . . . : Да
   Автонастройка включена. . . . . . : Да
   IPv4-адрес. . . . . . . . . . . . : 192.168.1.39(Основной)
   Маска подсети . . . . . . . . . . : 255.255.255.0
   Аренда получена. . . . . . . . . . : 17 мая 2020 г. 11:51:38
   Срок аренды истекает. . . . . . . . . . : 17 мая 2020 г. 13:26:39
   Основной шлюз. . . . . . . . . : 192.168.1.1
   DHCP-сервер. . . . . . . . . . . : 192.168.1.1
   DNS-серверы. . . . . . . . . . . : 192.168.1.1
   NetBios через TCP/IP. . . . . . . . : Включен

route print

IPv4 таблица маршрута
===========================================================================
Активные маршруты:
Сетевой адрес           Маска сети      Адрес шлюза       Интерфейс  Метрика
          0.0.0.0          0.0.0.0      192.168.1.1     192.168.1.39      5
         10.0.0.0        255.0.0.0     192.168.0.11     10.10.10.184     11
     10.10.10.184  255.255.255.255         On-link      10.10.10.184    266
   88.204.102.194  255.255.255.255      192.168.1.1     192.168.1.39      6
        127.0.0.0        255.0.0.0         On-link         127.0.0.1    306
        127.0.0.1  255.255.255.255         On-link         127.0.0.1    306
  127.255.255.255  255.255.255.255         On-link         127.0.0.1    306
      192.168.0.0    255.255.255.0         On-link      10.10.10.184     11
    192.168.0.255  255.255.255.255         On-link      10.10.10.184    266
      192.168.1.0    255.255.255.0         On-link      192.168.1.39    261
     192.168.1.39  255.255.255.255         On-link      192.168.1.39    261
    192.168.1.255  255.255.255.255         On-link      192.168.1.39    261
        224.0.0.0        240.0.0.0         On-link         127.0.0.1    306
        224.0.0.0        240.0.0.0         On-link      192.168.1.39    261
        224.0.0.0        240.0.0.0         On-link      10.10.10.184    266
  255.255.255.255  255.255.255.255         On-link         127.0.0.1    306
  255.255.255.255  255.255.255.255         On-link      192.168.1.39    261
  255.255.255.255  255.255.255.255         On-link      10.10.10.184    266
===========================================================================
Постоянные маршруты:
  Сетевой адрес            Маска    Адрес шлюза      Метрика
      192.168.0.0    255.255.255.0     10.10.10.184       1
===========================================================================

Офис 2:
Public IP: static - ip 83.172.xx.yy
Local IP: 192.168.0.0/24
Адрес Mikrotik: 192.168.0.1

Answer 1

Set the bridge MTU to 1500.

Maximum transmission unit, by default, the bridge will set MTU automatically and it will use the lowest MTU value of any associated bridge port.