Nilo

I agree, and that what happens if I drag or insert the 48k file into the 44.1k project, but apparently this is not the case when a custom template already includes a track with a certain sample rate. In my case I start a 44.1kHz project, that already includes a 48kHz track from the saved custom template, and the program doesn't warn against this sample rate mismatch!

I believe I've identified the source of this problem, hopefully! The main difference between the custom and built-in templates lies in that the custom template includes an audio track named "noise floor." This track contains a recording of the background noise in my recording room, which serves as a base for my VO. When I edit the audio to remove unwanted breath sounds, this "noise floor" track fills in those gaps with background noise, ensuring that the audiobook meets the required standards. This "noise floor" file included in the custom template has a sample rate of 48,000 Hz. When I created a new 44.1 kHz project using the problematic template but removed the "bed" track before saving it, the issue disappeared, and the project maintained the 44.1 kHz sample rate. So, could this "mixed sample rates" be the root cause of the problem?

Thank you both @David Baay and @John Vere. I usually record at 48 kHz and then export my audio files at 44.1 kHz and 16-bit, which is the required format for audiobooks. However, I recently had a project with a substantial recording, with Part One alone spanning over 2 hours, divided into three separate files. To maintain consistency and reduce the file size and CPU load on my relatively slow PC during the editing process, I decided it would be better to both record and edit the project at 44.1 kHz from the beginning. [I would like to point out that Pro tools Intro, the free version, handles the 3 files at once, on the same PC, very nicely and smoothly, but I am just not familiar with it as I am with CbB that has also all my presets]. The issue I encountered didn't arise during the recording phase; instead, it occurred during the editing process. The audio files were originally recorded elsewhere at 44.1 kHz using my Behringer UMC22 Audio Interface and were subsequently imported in CbB on a different PC (for editing). That is: the imported file is 44.1 kHz, the new project created in CbB is also 44.1 kHz 16-bit as shown in the transport module, I do all my editing without any problem, save my work, but when I reopen it, it shows 48kHz 16-bit, the waveform's gone, and when I try to recompute picture, there is no associated audio file there! In this scenario, I think, the audio interface isn't at play, or is it? Here's some screenshots:

As indicated in the title, CbB's default setting is 48 kHz, which matches the sample rate of all the devices on my PC, to change this, I use the New Project dialog to create a 44.1 kHz project through a custom template designed for audiobook auditions. While I can work without issues in this setup, a problem arises when I save my work and reopen it at a later time – the project opens at 48 kHz, and the waveform is replaced by a flat line. Interestingly, if I perform the same process but create the project using one of the built-in templates like Basic or Empty, it retains the 44.1 kHz sample rate. As far as I know, project templates should not alter the project's sample rate. This behavior is consistent with the built-in templates, where the sample rate remains unchanged. However, there appears to be an issue when using custom templates that results in a sample rate override. I would appreciate any guidance or assistance in resolving this matter.