Actually with the new 7.10rc6 update the connection works well and fast, no crashes whatsoever, but the log says constantly:

Jun/20/2023 22:00:51 interface,info lte1 link down
Jun/20/2023 22:00:51 interface,info lte1 link up
Jun/20/2023 22:05:01 interface,info lte1 link down
Jun/20/2023 22:05:01 interface,info lte1 link up
Jun/20/2023 22:08:11 interface,info lte1 link down
Jun/20/2023 22:08:11 interface,info lte1 link up
Jun/20/2023 22:11:11 interface,info lte1 link down
Jun/20/2023 22:11:11 interface,info lte1 link up
Jun/20/2023 22:12:31 interface,info lte1 link down
Jun/20/2023 22:12:31 interface,info lte1 link up
Jun/20/2023 22:15:02 interface,info lte1 link down
Jun/20/2023 22:15:02 interface,info lte1 link up
Jun/20/2023 22:15:31 interface,info lte1 link down
Jun/20/2023 22:15:31 interface,info lte1 link up
Jun/20/2023 22:17:01 interface,info lte1 link down
Jun/20/2023 22:17:01 interface,info lte1 link up
Jun/20/2023 22:22:14 interface,info lte1 link down
Jun/20/2023 22:22:14 interface,info lte1 link up
Jun/20/2023 22:23:24 interface,info lte1 link down
Jun/20/2023 22:23:24 interface,info lte1 link up
Jun/20/2023 22:26:34 interface,info lte1 link down
Jun/20/2023 22:26:34 interface,info lte1 link up
Jun/20/2023 22:28:14 interface,info lte1 link down
Jun/20/2023 22:28:14 interface,info lte1 link up
Jun/20/2023 22:30:54 interface,info lte1 link down
Jun/20/2023 22:30:54 interface,info lte1 link up
Jun/20/2023 22:32:24 interface,info lte1 link down
Jun/20/2023 22:32:24 interface,info lte1 link up
Jun/20/2023 22:33:24 interface,info lte1 link down
Jun/20/2023 22:33:24 interface,info lte1 link up
Jun/20/2023 22:39:24 interface,info lte1 link down
Jun/20/2023 22:39:24 interface,info lte1 link up
Jun/20/2023 22:50:35 interface,info lte1 link down
Jun/20/2023 22:50:35 interface,info lte1 link up
Jun/20/2023 22:53:08 interface,info lte1 link down
Jun/20/2023 22:53:08 interface,info lte1 link up
Jun/20/2023 22:57:37 interface,info lte1 link down
Jun/20/2023 22:57:37 interface,info lte1 link up
Jun/20/2023 23:01:17 interface,info lte1 link down
Jun/20/2023 23:01:17 interface,info lte1 link up
Jun/20/2023 23:02:07 interface,info lte1 link down
Jun/20/2023 23:02:07 interface,info lte1 link up
Jun/20/2023 23:03:27 interface,info lte1 link down
Jun/20/2023 23:03:28 interface,info lte1 link up
Jun/20/2023 23:03:38 interface,info lte1 link down
Jun/20/2023 23:03:38 interface,info lte1 link up
Jun/20/2023 23:12:32 interface,info lte1 link down
Jun/20/2023 23:12:32 interface,info lte1 link up
Jun/20/2023 23:14:36 interface,info lte1 link down
Jun/20/2023 23:14:36 interface,info lte1 link up
Jun/20/2023 23:16:35 interface,info lte1 link down
Jun/20/2023 23:16:35 interface,info lte1 link up
Jun/20/2023 23:17:56 interface,info lte1 link down
Jun/20/2023 23:17:56 interface,info lte1 link up
Jun/20/2023 23:20:15 interface,info lte1 link down
Jun/20/2023 23:20:15 interface,info lte1 link up
Jun/20/2023 23:20:56 interface,info lte1 link down
Jun/20/2023 23:20:56 interface,info lte1 link up
Jun/20/2023 23:23:34 interface,info lte1 link down
Jun/20/2023 23:23:34 interface,info lte1 link up
Jun/20/2023 23:24:55 interface,info lte1 link down
Jun/20/2023 23:24:55 interface,info lte1 link up
Jun/20/2023 23:26:16 interface,info lte1 link down
Jun/20/2023 23:26:16 interface,info lte1 link up
Jun/20/2023 23:30:06 interface,info lte1 link down
Jun/20/2023 23:30:06 interface,info lte1 link up
Jun/20/2023 23:32:06 interface,info lte1 link down
Jun/20/2023 23:32:06 interface,info lte1 link up
Jun/20/2023 23:33:55 interface,info lte1 link down
Jun/20/2023 23:33:56 interface,info lte1 link up
Jun/20/2023 23:37:35 interface,info lte1 link down
Jun/20/2023 23:37:36 interface,info lte1 link up
Jun/20/2023 23:42:05 interface,info lte1 link down
Jun/20/2023 23:42:05 interface,info lte1 link up
Jun/20/2023 23:44:36 interface,info lte1 link down
Jun/20/2023 23:44:36 interface,info lte1 link up
Jun/20/2023 23:45:16 interface,info lte1 link down
Jun/20/2023 23:45:16 interface,info lte1 link up
Jun/20/2023 23:46:37 interface,info lte1 link down

Then it stops maybe for 30 minutes.. and starts again to link up and down
The weird part is that when connected with B3+N78 it doesn't do it. Maybe is my provider?

Thanks everybody

You might want to add a logging topic to get some more data on what's happen between those messages. You can use "/system/logging/add topics=lte,!packet" which should more logs. It very well could be a bug, but the additional logging is what Mikrotik would need. And maybe it provide some clue before that.

Also there is a 7.10 stable you might want to try, but doubt it change much from rc6 here, but maybe...