Since I've installed some extra libraries, perhaps by some Russian guy ?
So, Putin hacked your LTspice?!

To select a transistor, first place the symbol for a npn in the schematic, then right click the newly place npn, and press "Pick New Transistor" button. A list of transistors should open, with many columns. To sort that list alphabetically (by the column you want), click the header of that column. First column is part number, second is the manufacturer, and so on. If you click the same column header again, it will sort in the descending order.
For example, click the header 'Manufacturer' (the second column), then scroll down to NXP. You should see the BC547, between other NXP transistors. Or, you can click the header 'Part No.' of the first column, and sort by the transistor name, then scroll down to the BC547.
If you don't have the BC547 any more, it means the additional library was not installed properly.