Since two weeks users are telling me that nearly each day existing leads/opportunites are not in our Odoo 12 system any more.

On the first day, I thought, this must be a mistake! But now we are tracking and reporting our opportunities and we can see that every day opportunities are missing!! I tried to find the opportunities directly in the database, but the opportunites are not existing anymore. Even in the case when an opportunity had already a sales quotation, unbelievable the quotation exists, but the opportunity has been deleted!! Inour case, each quotation must have a sales opportunity.

I am at a los!

I decided to have a look into the odoo-server.log. Here I found for e.g. following entries

2019-10-18 08:45:23,516 22950 INFO server odoo.addons.base.models.ir_cron: Starting job `Base: Auto-vacuum internal data`.
2019-10-18 08:45:23,555 22950 INFO server odoo.models.unlink: User #1 deleted bus.bus records with IDs: [118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134]
2019-10-18 08:45:23,639 22950 INFO server odoo.addons.base.models.ir_attachment: filestore gc 33 checked, 3 removed
2019-10-18 08:45:23,710 22950 INFO server odoo.models.unlink: User #1 deleted mail.wizard.invite records with IDs: [2, 3]
2019-10-18 08:45:23,750 22950 INFO server odoo.models.unlink: User #1 deleted mail.compose.message records with IDs: [58, 59, 63, 64, 66, 67, 57, 60, 61, 62, 65]
2019-10-18 08:45:23,820 22950 INFO server odoo.models.unlink: User #1 deleted mail.message records with IDs: [3784, 3783, 3779, 3778, 3766, 3745, 3744, 3662, 3661, 3497, 3496, 3495, 3486, 3485, 3104, 3103]
2019-10-18 08:45:23,896 22950 INFO server odoo.models.unlink: User #1 deleted ir.model.data records with IDs: [12621, 13148, 12464, 12609]
2019-10-18 08:45:23,923 22950 INFO server odoo.models.unlink: User #1 deleted crm.lead records with IDs: [124, 124, 106, 52, 94, 124, 124, 106, 106, 94, 94, 94, 94, 94, 52, 52]
2019-10-18 08:45:23,953 22950 INFO server odoo.models.unlink: User #1 deleted mail.activity records with IDs: [130, 133, 131, 132]
2019-10-18 08:45:23,977 22950 INFO server odoo.models.unlink: User #1 deleted mail.followers records with IDs: [2907, 3081, 3082, 3170, 3212, 3213]
2019-10-18 08:45:24,003 22950 INFO server odoo.models.unlink: User #1 deleted crm.lead records with IDs: [106, 124, 94, 52]
2019-10-18 08:45:24,058 22950 INFO server odoo.models.unlink: User #1 deleted mail.mass_mailing.test records with IDs: [1, 2]

As we can see, the systen deletes my crm.leads records! 

What's going on here? Can anybody help?