Steps to reproduce:

1. Install Zabbix Server 7.0.0alpha7 or 7.0.0alpha8 (May be earlier. 7.0.0alpha4 is working OK)
2. Add host with Zabbix Agent older than 4.0 (tested with 3.4 and 3.0)

Result:
Zabbix agent is not available

There are messages in zabbix agent log: "Message size 12884901898 from <MyServerIp> exceeds the maximum size 134217728 bytes. Message ignored.​"

Discussion on forum: https://www.zabbix.com/forum/zabbix-feedback-for-alpha-and-beta-versions/473229-upgrade-from-zabbix-7-0alpha4-to-7-0alpha7-broke-many-zabbix-hosts